I will say that although I haven't done huge projects involving Toontrack, I've done about 1/2 dozen short ones and I've not experienced any problems.  I'm not reading about the problems that konradh has mentioned above.  But I certainly won't disbelieve he is not having them...or other people as well.  But over in the Toontrack forums, they're not talking about these issues.
 
I DID have the problem of EZD2 *hogging* the midi outputs of other softsynths when opening older projects that had EZD in them, but that was an easy fix of just re-assigning them.
 
I will have to try freezing some synths, etc to see what's up.  I will say, I have opened projects with frozen Toontrack stuff in them, and didn't notice any problems.

It appears there might be something that's throwing a wrench into things, other than just Sonar/Toontrack working together.... like the sampling rate thing.  Something kind of hidden under the hood, so to speak.  Otherwise, I'm sure there would be huge amounts of complaints, loud and clear...which I'm not seeing when reading the forums.

But, that doesn't help konradh... and I hope the solution comes quick for his sake.

I've fixed weird problems after installing new plug-ins with the reset/rescan routine. Maybe worth a try.

The only *weird* plugin is Toontrack's EZX Electronic  :-D  !!!!  I like their new GUI, but the old one was off the "mothership".  Pretty crazy, I'll say!

 Actually, that's the primary kit/reason that I use EZD.  Otherwise it's Superior.
 
oops...you said "weird PROBLEMS"....not weird plugs!!
 

As Craig has mentioned, I have seen the results of two independent teams working to solve an issue between a host and a 3rd party plugin.  It happened early as I came on to the Toontrack betatest team.  I can't recall what it was exactly but because of my report, Toontrack implemented a change in EZdrummer to accommodate a SONAR behavior and almost simultaneously Cakewalk implemented a change to accommodate the EZdrummer behavior and they ended up cancelling each other out and causing other issues.
 
If the softsynth output issue can be resolved by individual users making a manual change in their projects, I'm thinking it would be better to do that than to open a can of worms to fix legacy issues that could snowball into problems for all the other softsynths down the line.
 
My $.02

mixmkr
The only *weird* plugin is Toontrack's EZX Electronic  :-D  !!!!  I like their new GUI, but the old one was off the "mothership".  Pretty crazy, I'll say!

Actually, that's the primary kit/reason that I use EZD.  Otherwise it's Superior.
 
oops...you said "weird PROBLEMS"....not weird plugs!!
 

Haha.  I've always hated that GUI.  (But I'm not into EDM, so take that with a grain of salt.)

To clarify, I was not being critical of Cake.  I have developed a lot of software and I know how complex this is.  I just wish Toontrack or Cake would give us a status.
 
As for my problems, they are repeatable and have been replicated by Sweetwater.  The fact that we don't see them on the Toontrack forum is not really indicative since Toontrack has not been updating the forum consistently and it leaves posts in "awaiting moderation" mode for weeks.
 
At this point, I am going to get a refund for the upgrade and buy additional drum kits for Kontakt.

Ultimately it is on Toontrack to test their updates on various DAWs.
For me, this puts up red flags for purchasing a Superior Drummer update as well when that comes out.

Hill62
Ultimately it is on Toontrack to test their updates on various DAWs.

Indeed, this is the usual protocol. We often have manufacturers contact us for a copy of Sonar they can use to test their plug-ins, ReWire compatibility, etc. If you think about it, it's much easier to test a plug-in with a very finite number of DAWs then to test a DAW with a virtually unlimited number of plug-ins.
 
It's generally considered inappropriate to have one company beta test another company's product. This isn't just a matter of courtesy, but for competitive reasons the manufacturer might not want to divulge details of a new product while it's still being developed.
 
This doesn't rule out companies working together to solve problems, but that usually happens after the product is out, or an update occurs during a product lifetime that breaks compatibility. 
 
There is one exception because I remain on good terms with many software developers. They will test their products with Sonar but they are not always Sonar experts. If I'm a long-term user of their products, sometimes they'll make sure I have a copy because they know I'll put it to real-world use and will report back on the results.

I bought EZ Drummer 2 upgrade from 1 a few weeks ago.  Big time problems!  I'll never buy anything from Toontrack again!  This thread started a year ago and obviously the situation, at best hasn't improved or has gotten worse.  Existing projects containing Aria Player (Garritan) and even SI Bass guitar find these instruments muted.  NI Session Strings seem to work OK, but I wanted to try some new EZD2 features on existing projects.  Also, there's a linking problem in Sonar and nobody either at Toontrack nor Sweetwater has any clue why.  Every time I launch EZ Drummer 2 in Sonar I get an error saying that this isn't the latest version and that the latest version can be found at C:Program Files(86)/VSTPLUGINS.  Even though the Ezdrummer.dll is there at that location and is the latest version I get the same damned error message and the Search-Tap feature doesn't work. The damned installer doesn't tell you where it's installing the plugins and Windows 8 Search function SUCKS! I'm ready to quit this hobby.  Seriously!  If these software developers can't do any better than this I'm tossing all my gear.  I'm sick of wasting good money on programs like this that cause so much trouble and frustration.  I can think of better and more useful ways to spend my money.
 
John B.
 
PS-These a$$hole software vendors won't give refunds for software either.  I used to understand why they didn't, but now they make you authorize every computer you use it on on their online database so they can simply not authorize you if you don't have a valid serial #.  All this and they still deny refunds in situations like this.  They just don't want to refund you anymore and they still have the gall to use software piracy as an excuse!

I have EZ Drummer 2.  I don't use it on every project, but I didn't have any issues with it and Sonar.  Am I in for a rude awakening?