Grace notes after the note
It looks like this was implemented and is now broken again in nightly builds. I searched but did not find the issue reopened anywhere, or any bug report on the new error. Just checking.
This is used fairly commonly in some music, and it's not just for trill endings. There's more discussion here: http://musescore.org/en/node/10039 . There are several workarounds, but I think it's a fair statement that none is completely satisfactory.
I notice that LilyPond implements grace notes after the note with an \afterGrace command, and Music XML implements it with a 'steal-time-previous' or 'after-grace' command. (See http://www.lilypond.org/doc/v2.17/Documentation/notation/special-rhythm… and search the page for "afterGrace".)