I've just googled the problem, and it seems to be some kind of bug!
Apparently there are loads of problems with this updated facebook app:
- Broken profile pictures,
- Refresh problems,
- Can't see old messages in the inbox or sent,
- Can't view events,
- Can't see birthdays,
- Can't see people's info.
I hope they get this problem fixed.
One solution we could try would be to uninstall the FB app and install the older version?