We have a situation where we have a date field and are using a secondary "is between" filter and it does not have a label for the "min" field. I'm not clear if this is totally a BEF issue, but I have found a simple way to fix it. So the BEF filter looks roughly like (warning, psuedo-array!):
array( '#title' => 'BEF label', 'min' => array( '#title' => '', // ... ), 'max' => array( '#title' => 'And', ), )
So this renders the "min" text field with no label, then the "max" textfield with an "And" label. The patch attached below looks to see if there is a "min" item and adds the title if it's blank. I'm not sure if that's the best way to fix this so let me know.