Sonar producer X3e
Melodyne editor 2.12 retail
I noticed this start happening about 4 weeks ago or so.
After I add melodyne editor as a region effect and I go about editing the blobs in Melodyne, the X3 "stop" button (on the transport module, on the Control Bar) gets grayed-out and can't be activated with a mouse click. The "stop" button looks like it was pressed and got stuck. The button doesn't release. The space-bar still works to start/stop playback, even when the "stop" button is stuck.
 
I have done a complete re-install of both Sonar and melodyne in case there was some type of corruption but it didn't help.
 
Also, (FWIW) once in a blue moon Sonar will crash at startup and if I look at the dump information it will indicate that Melodyne was the problem.
 
If anybody has any suggestions to try I can try tonight and post back my findings.
Thanks.
 

More information:
I loaded the project in safe mode with no plug-ins except Melodyne and it worked properly.
The "stop" did not get grayed out and no amount of starting/stopping/editing could make the problem reoccur.
So perhaps there is a conflict with Melodyne and another plug-in.
Now I'm off to eliminate suspect plugs one at a time 'till I find the bad one. 
 

Moved to the Sonar forum for troubleshooting. I can't reproduce at my end.
 
I would look at plugins, also update audio interface to the latest driver + firmware.
 
Ta.