This item might already be posted - forgive me if it has, I haven't found it.
It is reported as a bug in tracker mdl-3721 .
My problem occured when editing wiki pages with large tables - they quickly became huge. Cleaning up is very tedious - I have a total of about 500 pages.
I have managed to fix the symptoms by adding a line to the wiki engine - I'd love someone more knowledgeable than me (must be lots of you out there!) to have a look at the code and see if the bug can be fixed properly.
I've added a comment to tracker showing the patch.