Line 631 of inc/maintenance.php has:
if(count<cols[quest][2])
{ width = parseInt( %POLL-WIDTH% / cols[quest][0]);
basically if POLL-WIDTH is empty for whatever reason, the js is interpreted as a regex (which would be invalid) i.e.
parseInt( / cols[quest][0] )
PHP side it should probably have a default value or check for null, user side just make sure your poll has a width.
