Game Player - Mixing Engines in Playlists - Bugs Galore
You currently can not safely mix game types that span different engines in playlists: this currently includes
The emulator of the previous type does not shut down,
When switching from MESS to MAME, the engine does not fully reset its state and tries to launch MAME with some MESS parameters.
In short, It's a tangled mess, which can be solved by refactoring the whole damned thing, now that we have a few different engines to target. ARGH.