Possible tremolo bug

I'm not familiar with this - could someone help me with a possible report?

In both:

1. Open attached file.
2. Select first note.
3. Double-click 'between stem' tremolo.

Result: There is a minim rest between the two minim notes in a 4/4 score - should step three be allowed in this situation?

In 1.1:

4. Save.
5. Close.
6. Re-open.

Result: The rest between the notes has disappeared.

Using MuseScore 1.1 and 2.0 Nightly Build (5290) - Mac 10.6.8.