Sounds like it could be bug #93633 that should be fixed in EPiServer 7 - patch 1: http://world.episerver.com/Articles/Items/EPiServer-7---Patch-1/
Thanks for the help!
Is there any way to fix this untill we update? Other than readd the blocks and republish the pages?
We got a strange problem today. All the blocks are gone from the pages, both on the live page and in the cms.
If you go to the blocks however they still indicate that any changes made to them will effect the page they should have been on.