From a vanilla Drupal 7 install, with a MySQL database and only ctools and views modules added beyond core, add a filter to a view on any numeric field (nid is usually available ;-> ) and select "Regular expression" as the operator.
The resulting SQL will include:
nid RLIKE '', '', ''
The extra quoted strings before the value we care about make SQL sad.
This appears to be happening because views_handler_filter_numeric::value is an array with 'min', 'max' and 'value' elements, of which only the third is applicable here.
The fix appears to be fairly simple (select only the array element we need, 'value'), and I've attached a diff thereof.