Calendar meeting room items are blank (blue)

Hi,

Some of our users in a subdomain are having problems viewing booked meetings in 6 of 8 rooms.
They appear blue with no info, if you hover the cursor over it, the info appears in the hover box.
See picture: http://desmond.imageshack.us/Himg209/scaled.php?server=209&filename=outlookcalendar.jpg&res=landing
(the working items are blurred out)

This happens in all views, and I think after the users and rooms were moved from Ex2003 to 2010.

I see everything fine in all rooms, although I can reproduce some of it by quickly scrolling back and forth the dates, then some of the objects turn blue.

Any idea what can cause this? We have tried to make a new account in the subdomain, but it works fine.
I guess it could be either the user accounts or the room accounts. Anyone seen this before?

Thanks.