TinyMCE behaving strangely after upgrade

I upgraded from 2.4.1 to 2.5+ recently and the TinyMCE toolbar isn't behaving normally.  The toolbar only appears when editing is turned off - they I can go to 'Edit Settings' or edit a question and it's there. However, if I turn editing on the toolbar is missing completely in activities, labels, questions, everywhere...  Is this an intentional change, or is there a setting which is causing this behaviour, or did something go wrong during the upgrade?

Thanks,

Boris.