I installed ukeyboard, rebooted, disabled QtLockscreen, Qalendar and camkeyd, but it made no difference. Camera Lens Launcher was probably the only non-standard thing running in the background at that time. After tinkering with ukeyboard settings I discovered that with some layouts Ctrl+Space language switching doesn't work at all, and that's it.

Seeing no objections to the new shortcut, I've uploaded an update, although it's Ctrl+L instead of Ctrl+P, because the related Ctrl+Shift+P would cause another collision. The changelog for OMP 20140307-1:

• Fixed a bug that could cause incorrect opening of playlist files via mime_open and inability to restore the old music playlist.
• Modified all shortcuts using Ctrl+Space to use Ctrl+L, to avoid confusion (and collision?) with a Maemo system shortcut.
• Restored a phrase accidentally removed from the German translation.

I think it actually depends on the kind of the assigned playlist rather than on whether OMP is running. For example, if you were listening to music and then decide to watch a video podcast, even without closing OMP, the transition would trigger the bug. If that's the case, the bug should be fixed now.