The placement of post-grace notes is screwed up. Sometimes the note overlaps the original note when the measure is small, and sometimes the note is far extended from the anchored note/chord. Somehow the measure size isn't altered on default positioning, and if the user tries to accommodate it by chord-offsetting, the measure stars to shift in undesirable ways.
One example of this is found here: https://musescore.org/en/node/293082
And another example showing how acciaccaturas working fine, but post-grace notes don't work fine when they should work not exactly of course but similarly: