NOTE: I am not asking how to fix this. I do not need help fixing this. I am sharing a curious bug I found, with the steps to reproduce it.
This is in regular 4/4. Force Duration is switched off, and so is Insert Mode. Start with three separate tremolo whole notes:
Tie them together:
Now, the total duration of this note is a dotted breve. Select it, hit . to make it undotted. The result is this:
Similar behaviour occurs with shorter note values, and with different tremolo values.
Oddly enough, when starting to add notes to the situation above, this happens:
When the notes are tied together before the tremolo is added, everything behaves as expected.