[quote="Lowlander"]Are you deleting from the PC as well?[/quote]
That was my intention. Actually, I'm going to withdraw this, as I haven't been able to duplicate it since. While a track is playing, no matter whether I right-click and select Remove from the context menu, or tap Del while it's playing, I get the dialog box asking whether I'm sure I want to delete it, and the radio-button alternatives of Library only or Library and Computer. If I select the latter, the track's immediately deleted and play continues to the next track, as it's always done. Not sure what happened originally, but all seems to be well now. Sorry about that...

Are you deleting from the PC as well?

If I delete a track in MM while it's playing, in the past, MM would always immediately stop playing it. This is not happening in v. 4.06.1501 - the file disappears from the library, but MM keeps playing it.