If I insert an extra bar in just one part (get the insert caret, select ‘insert bar rest’), all the notes correctly shift relative to the the other parts. But the dynamics remain where they were.
Is the expected behaviour? If so, it is a bit unfriendly!
It is, for now at least, because when you insert time, you insert it only into the active voice, and dynamics are not (by default) attached to a particular voice, but rather to the instrument as a whole. We will expand upon this behaviour in future versions to try to make it more useful in more circumstances.