Unfortunately we know this problem for a few weeks with the beta version. Apple changed several important elements that prevents QT to work correctly in Yosemite. We will work to correct this problem as soon as possible (probably late November). Thank you for your patience.
Only workaround at the moment is to rollback to OS X Mavericks. This can be done, but might be a tad painful.
Update (24th November, 2014)
Looks like January of 2015 is when Open-Sankoré is most likely to be updated (according to this post) to work with OS X 10.10 Yosemite.