Accidentals incorrect after courtesy accidental when changing key signature

MuseScore 1.1, Windows Vista.

Steps to reproduce:

1. Open attached score
2. Drag Eb major key to first measure

Expected result: the second half note in measure 2 should have a flat sign in front - it's a Bb occurring after a B natural.

Actual result: no flat sign appears, making it read as B natural. It still plays as Bb, however, and if you select all and ctrl-up / ctrl-down to transpose up and then back down an octave, the flat sign appears.

This only happens in measures that include a courtesy accidental, and it only happens for notes that are actually affected by the key change. That is, had the original file been Db, D natural, Db, there would have been no problem.