Hmm, I've found that this also seems to happen when Chainer is set to bypass in different ways. At least, I think so. It seems that when I allow the track to end "naturally" (play to the end), it quits quite happily, without crashing. But if I stop the track midway, or just close it, it'll 9 out of 10 times die.
I can load a song, then immediatelly after close it, and mpt is gone.
Additional note which Relabs knows already, but is worth a mention: If you make changes to such song, and then press close, MPT asks if you wants to save the changes. If you say yes, mpt closes, but the changes were saved.
Also, it doesn't always happen. With that I mean: I have songs that use xlutop chainer that do close normally.
In fact, In my testcase I did the following to reproduce:
Made an empty song and added the following plugins in that order, in which after each add, I saved and closed.
15x xlutop (empty)
Then randomly chosen one of the 15 xlutops and added the following plugs:
2x mda stereo
1x G-Amp Classic <- crash.
So I thought, gotcha. Made a new song with 1x xlutop, 1x mda stereo and 1x G-Amp Classic, no problem there.
It might very well be that xlutop itself crashes causing mpt to crash.