Incorrect actual duration

1. Open attached score.
2. Right-click the anacrusis on the Drums stave.
3. 'Bar Properties...'/'Measure Properties...'.

Desired result: The actual duration is listed as 6/8.
Actual result: The actual duration is listed as 5/8.

Note: 1.3 has the same 'Actual result', despite the appearance of the 'Desired result'. If you play the score, the final crotchet (quarter) in the anacrusis plays the length of a quaver (eighth).

Discussion: I'm not exactly sure how the issue came about, but I think the score was produced in either 1.2 or 1.3. Matters are complicated due to the Electric Piano having an actual duration of 5/8.

Using MuseScore 2.0 Nightly Build (e10f6b5) - Mac 10.7.5.