Not sure if this is a new issue, but with the new Cambridge bug for 'paste special', where a paste goes into a new clip, and has the same name of the copied-from midi clip:   you need to change the name of that pasted clip, for sanity .. and "clip properties" no longer is in any menus that I can find. 

Clip properties has been gone from the context menu for a long time; it's all under the Clip tab of the Track Inspector. You're saying the "Paste into existing clips" option isn't working for you? Not a problem here.
 
EDIT: I posted the solution in your other thread: Click the Advanced button to see the full Paste dialog. Not a bug.

brundlefly
You're saying the "Paste into existing clips" option isn't working for you? Not a problem here.
 
EDIT: I posted the solution in your other thread: Click the Advanced button to see the full Paste dialog. Not a bug.

Based on the info in the other thread, I thought his issues might be due to the difference between trying to open a MIDI clip as a project and trying to import it (e.g., from the browser). But I may have misunderstood the finer points of his scenario.

Just to clarify, re the "advanced" section of the Paste special.   In the case of the Bug, NO DIALOG (advanced or not), so that was not a fix, and was not relevant.  Thanks for the info about clip naming, I was looking everywhere for that.

WilliamCopper...you seem to be having issues that I solve by emptying the Pic Cache folder.  Your issues seem to be related to memory and buffers.
 

Regarding the Paste Special issue for which the other thread has been locked (?).
 
I would focus on the fact that you're not getting a Paste SPeical dialog. since we don't know what the paste special settings are, anything is possible in terms of where things end up, but the root of the problem is that you don't get the dialog. It seems like some process is intercepting the dialog and submitting it automatically with whatever settings were used last time. Do you have any 3rd-party apps installed related to creating custom keyboard shortcuts or auto-filling dialogs for you?
 
Also, do you have Move Over to Make Room set in your editing preferences? This is known to be broken, and seems it might be contributing to the issue when you paste multiple times to the same location. I recommend you change it to Blend.
 
And, finally, in which version of SONAR did this project originate? I'm thinking this kind of whacky behavior might be due to a project evolving through many versions of SONAR and having some project configuration/status flags out of sync - similar to the continuing issue I have with projects opening with all MIDI tracks showing Inline PRVs though edit filters are set to clips.
 
Is the original copy of the project still broken? I'd be interested in seeing how it behaves on my installation if you'd care to share it. I'm not familiar with any too-many-clips issues other than the large file sizes, RAM usage and related GUI slowness that can result from splitting drum tracks at transients, creating hundreds or thousands of slip-edited clips; do you have a thread reference for something not related to splitting at transients?
 

Here are some answers to your questions, brundlefly:
 
no 3rd party aps.   I have a couple of VST effects, is all: SIR2, a reverb, Soundstage2, another. 
 
I use "blend" for editing preferences, never changed it. 
 
The project I'm using now was originally created in Sonar 5, saved as a Midi Type 1 format file, and opened into Platinum.   I've gone through several saves as the project developed, so what I saw recently was from a project saved in platinum and re-opened for more work. 
 
No, when the same project, version 4 or 5, was saved in a new name, and sonar was closed, then re-opened, the paste special worked correctly.  
 
"too-many clips" in my experience is in the low hundreds, just from adding and deleting things to forty or fifty midi tracks.
 
 

Saving and opening as a .MID would eliminate any project format compatibility/corruption issues from previous versions. I think it must be a RAM problem... you have too much, and something got corrupted knocking around in all that empty space.