I know it sounds an odd question, but is there any possibility that brass reeds would use more air than steel reeds in an accordion?

I've got two cajun accordions: one with steel reeds (C) and one with brass reeds (Bb). Having checked the Bb accordion myself for leaks, and having had an expert also check for leaks, and having found none, the Bb accordion uses significantly more air (and is thus far more difficult to play) than the C accordion.

Any ideas, anyone?