Fermata duration not being respected by other instrument

I have a two instrument score with a fermata in one bar (below). It's configured for double the duration of the note it's above (so, six beats in this 3/4 score).

Here, the bottom instrument (piano) plays for the correct duration, but the top instrument (vocal) seems to start to rush ahead around beat 3. This ends up meaning that the bottom chord continues playing over the next bar of both piano and vocals.

It worked when I first set it up. It worked for a while, but then I changed something (no idea what, but it wasn't anything related to the pictured bar) and suddenly it stopped working.

Also, if I click a note in the second bar on either instrument and hit play, it plays the chord from the previous bar as if it thinks it's part o the current bar, as well as the stuff in the second bar.

Is this something anyone else has encountered? Is there a way to reset this behaviour somehow?