Being a little more specific:
When the Facebook Plugin is active, the "New Post" (and the 'Posts' too) page on wp-admin takes a lot of time to load. And when it loads, the categories are not shown - I can't also schedule or even save a draft.
But when it comes about a previously saved post, everything works normally
I'm using the GitHub version - this was happening already with 1.02. Don't know if it's because the 3.4.1 wordpress update