Videoscore Bug

Hello,
I have two videoscores that I was able to create without any problems (http://musescore.com/node/115772 and http://musescore.com/node/115770), but with the third one (http://musescore.com/node/115593) I keep getting a weird error (on IE, FF, Chrome, Opera and Safari, so it must be related to either the MS score or the website itself; the scores were created with MuseScore v. 1.3, rev. 5702 on Windows 7).
When I try to edit the videoscore the music starts, but after a measure, when I press spacebar (or click on the next measure) the usual blue bar (the measure change marker) gets added at the very end of the song, instead of the current position. This also means that the measure tracker (the large pink highlighter) does not advance, because the "next measure" marker is defined at the very end of the piece. Since the entire song is thus perceived as measure one, I can then no longer click on any measure to add another marker: if I do, the pink highlighter goes to that measure but then instantly reverts to measure 1.
Now if I stop the song, delete all markers, rewind, then press play again, I can click on a measure, the pink marker advances, but no blue line gets added whatsoever.
Has anyone ever encountered this before? Can it be related to the score? All three scores were produced in the exact same way, same with the three youtube videos. They should all therefore behave similarly.
Thanks!