On a system where you are able to reproduce the problem, can you export the toolpaths using another postprocessor (e.g. GCodeMM)? Just ruling out things here. I'm unable to reproduce any of this here.

Since last summer I experienced on several occasions sudden QCAD deaths and PC stalls while using QCAD. Question; what was I doing?; a program error should be reproducable. It took an awful lot of time and patience for restarting and retesting Kubuntu and QCAD over and over and over and over again. Time after time experimenting with different sequences of action; still, the errors were not reproducable. As a final solution I even updated the mainboard (and its memory). And behold, even that was not the solution. OK. So, I took some old PC's from the attic, and created my own benchmark. It took me an awful lot of time and patience to execute the several tests on the real physical computers.

To my experience the Regenerate Toolpath routine claims memory but does not free it all times when closing. Some computers however are fine, but on several totally different computers this 'misbehave' is reproducable. I do not know why. I do know it does. This memory misbehave also explains all the previous QCAD-errors I have stumbled over; what seems random errors are in fact memory issues. The benchmark also tells several random computers showing the same 'misbehave', which means this issue is a little bit larger and therefore expands to a lot more users.

"If you don't know what is is, rule out everything that it isn't", (Mr Spock). So if you want to test for ruling out, its fine by me. Send me the testfile and I will try it.