bathroom vent

We live in a 40-story bldg and are experiencing a problem with the bathroom vent (no window). Most of the times (90-95%) the vent is not suctioning but is actually blowing in air bringing smoke and pleasant odors into our apartment. Management told us that nothing can be done because an imbalance between outdoor and inside pressure can actually reverse vent function. To us that does not make much sense because the vent is blowing in air nearly 100% of the times. Even opening a window does not help most of the times. Can any one tell us what the problem might be and how it can be fixed? Thanks.