I just closed SONAR, relaunched, instantiated the 3 FX, and tried to reproduce the cut off again and everything worked great. It does not cut off like it did a few moment before.  
 

I just tried a third time and found that the reverb tail playback was broken again. In this case, I deleted the EFX in the tracks feeding the bus and noticed immediately after that my bus no longer plays the bus reverb decay.
 
I thought, "a-hah, I'll put some EFX back on the source tracks"... so I did, but that didn't fix it.
 
I saved the broken project, closed SONAR, relaunched, and the bus reverb's decay is still cut off at the end of the source track's clips.
 
I am not sure why it is happening, but I do know that this would drive me crazy if I had Platinum installed on my DAW.

I just relaunched SONAR, and opened the broken project again.
 
I deleted one of the two EQ EFX I was sandwiching the Reverb with. As soon as I hit "Delete" the lost reverb tail played back for me.
 
 

What reverb plugin are you using.

Hi brundlefly,
FabFilter Q2 > Valhalla Room > FabFilter Q2

x64 VST2

Craig... yes, that looks like similar to what I am doing and what I described that's causing the problem.
 
"Always stream audio through effects..." is on. Changing the tail length setting to 10 seconds didn't do anything.
 
Stretching the tail of a short clip does not fix the problem. However, just to check... I set up a long clip on a 2nd track with a send to the reverb bus, so that it starts just before the 1st clip ends, then turned down the 2nd track to barely audible... and the reverb tail works for the first track... I'm guessing since audio continues to stream into the bus from the 2nd track.
 
However, that doesn't explain why putting a short or no decay effect before and after the reverb causes the problem in any case, and removing either of those short decay effects, the reverb tail plays fine.
 
I've reproduced the problem on my system using quite a few different plug-ins, including a long repeat delay... the delay also stops outputting once the input to the bus stops.
 
The CWB file I sent to Cakewalk that has the problem on my system, has a bus containing Channel Tools > Breverb 2 Cakewalk > Boost 11.
 
The bus stops output when either (1) the short audio WAV file ends on the track, or (2) on a long track... say, just after a snare hit... the bus send is automated to go to zero output... the bus output audio stops as soon as the bus send track automation goes to zero output.
 
Quite annoying, when you've been working on multiple projects, that are fairly busy... and you've thought for a while (weeks) things weren't sounding right... and just now realize... it's because some of the reverb/delay buses are no longer working correctly. And I really have no idea when exactly it started happening. Maybe when Aux Tracks and Patch Points were introduced? Or maybe earlier even. No idea, really.

Too weird... not all effects cause the problem. And some cure the problem.
 
For instance... I put in Channel Tools > Audio Damage Dubstation 1.5 > Boost 11... bus audio is cut off when clip ends.
 
Same chain... but put in NI Supercharger GT before the other effects... tails start working again.
 
I also have noticed so far the Channel Tools, Boost 11 before and after cause bus output to be cut off... and Sonalksis FreeG causes it.
 
Channel Tools > DubStation 1.5 > A.O.M. Invisible Limiter causes bus cutoff... reversing the order does not.
 
Just when you think Cakewalk and Sonar are getting their act together. Makes you wonder how many other processes within Sonar don't work correctly all the time. Processes that might be even harder to detect not working  correctly than this relatively easy one.
 
Maybe I should go back to learning Reaper again. 

Yes, what I was trying to explain about the symptoms I saw today is that simply adding or deleting anything from any of the EFX bins seemed capable of triggering or fixing the cut of reverb tail problem.
 
It may be specific EFX or it may be how SONAR handles any EFX.
 
FWIW I have been testing with an extra long 20 second reverb decay so the missing tail issue seems plainly obvious when it occurs.
 

I wonder if it relates to a mix of VST2 and VST3 plug-ins, where the VST3 versions turn off if there's no input. Might they be checking whether there's audio at the track input, not their input?
 
There has to be some rational explanation or way to reproduce every time. I sandwiched a reverb (the Sonitus) between two Channel Tools and there wasn't a problem. Maybe a different reverb would cause an issue?

I tried substituting either all VST2 or all VST3, to try to make sure any kind of mismatch between the way they turn the input on or off wasn't the problem. I reproduced the problem with all VST2 and all VST3.
 
But I wouldn't doubt that it has something to do with the way Sonar is handling a dynamic input to the VSTs on the bus. It just shouldn't have anything to do with shutting off the output of the bus based on receiving an input... ever. The output of the bus should only be shut off based on if any audio is being generated anywhere before the output.
 
And, in the reverb case, for instance,... it was definitely outputting the reverb effect until the end of the WAV clip (or bus send automation, as the case may be). It's just that the bus output stops immediately when the WAV file ends.
 
I dunno. WAY over my head, as far as the programming of it all goes.