yep, this was a fix that had to be patched into 7.5.6
original 7.5.6 has same problem

When I compare ubb_jslib.js and text_editor.js between 7.5.3 (my version) and 7.5.6 (this site), I find there are no differences?
Can you recall where the patch was applied? I'm more than happy to run the diffs and apply the fix myself.