Using both accent and staccato on the same note removes staccato's effect
bug is present in at least 3.4, perhaps in earlier versions too.
Reproduction of bug:
1) Put a staccato on a note.
2) Put an accent on the same note.
3) Use playback to play that note.
4) The note will sound accented, but not shortened.
Workaround: The "Accent-Staccato above" both accents and shortens notes. However, the accent on the accent-staccato also doesn't look the same as a regular accent, so using it for better playback means the aesthetic of the sheet music is diminished. (from different issue tracker)