Blank screen after posting contents containing 'HTML entities'

Upon submitting/previewing a post containing characters (which should be converted to HTML entities?) like é, ë and such the screen goes blank and does nothing.

Tried logging in and out, clearing the cache dir manually, disabling gzip. All with no results.

One of my Forum's users notes that after submitting a succesful post, and then submitting another one containing characters mentioned above everything seems to work fine.