It crashes in LAV because some D3D things seem to go wrong which were not checked properly, and i fixed those checks, you can grab a fixed version here:
http://files.1f0.de/lavf/LAVFilters-...1-gc82c1a0.zip
However, i was told that even with the crash resolved, it takes several seconds for playback to resume after a screen switch (which supposedly it didn't in previous versions). I can't reproduce, its fast for me (and it also didn't crash for me, i worked on a MPC-HC crash dump)
I suggest to follow madshis advice and test in which madVR version it started, or if any other external factors are involved.