I submitted a patch (not yet merged) for this over the weekend (when no bug tracking) so creating this now and will link the patch to here:
Short story: With the new SecurePoll logging system (\o/ yay) config pages (translation pages, poll creation/edit, voter eligibility) have summaries you can fill out when making a change which then become the edit summaries for the log entry. That log entry is stored in a wiki page (using the wiki edit summary) and so is limited by the size of an edit summary. Right now the input box accepts an unlimited amount of characters and just silently cuts the end off if it's over the limit. Limiting it to the normal max would make for less confused people when they don't see their full explanation and avoids having something important cut off by accident. [in theory the limit isn't actually 250 characters it's 255 bytes but this is the usual 'kinda' we use].