Thanks a lot! 
Removing the loop fixed the problem.
There probably should be a warning when this condition occurs rather than the whole thing collapsing. 
You are rght, but this is near impossible to check.
You could also produce a midi loop when using hardware.
Well, if you have GP configured to receive program changes on any device (or explicitly on the same IAC port) you’ll have a feedback problem if you use IAC
When the GUI breaks down like this, there will be some strange values in certain state objects. This could be used to trigger an alert that could give suggestions as to what the problem might be. It would be helpfull.
Except it doesn’t have to be the GUI that breaks down in this situation - totally depends what’s going on.
Yea, It’s a large piece of software so probably a pretty large task to track errors of various kinds. 