Thanks for the report, I'll look into this.
I have occasionally seen this too when using the spell checker, though it had seemed to be pretty rare. So if you're seeing it a lot on that page then it'll give me some clues to look at!
On a more positive note, I've made some good progress with understanding why we were sometimes getting errors when not logged in.
Thanks
Joe
cheers Joe and you are welcome
for clarity [no pun intended on the same named theme ] it only happened the once on that page
it happened quite frequently when editing other pages yesterday evening
hth