Page editor displaying unknown field""

I’ve just upgraded an org to 7.20, and in a number of pages, the page editor is not displaying field names correctly. For examole, I have tables whose columns appear as “Unknown field”; when clicked, its looking at the right field, and it even works correctly when using the page, but it makes editing a page more difficult. I can’t see anything untoward in the XML view, and its not just tables - I’ve seen it in a field editor in a pop up as well. I’ve just had an idea that it may have something to do with rendering options, but I’ll need to wait until I’m back at my laptop to check…