2 GPOs with firewall exceptions: one applies, one does not

I've run across what appears to be a strange issue in our Group Policy setup.

We have 2 GPOs set up to add firewall exceptions within our domain.  One has a firewall exception defined for program A; the other has a firewall exception for program B.  Both are linked to the parent OU where all our Windows 7 workstations reside within our Group Policy tree.

The exception for program A applies to these computers; the exception for program B does not.  If I move the firewall exception from the firewall exception GPO for program B into the firewall exception GPO for program A (so exceptions for both A and B are in the same GPO), the exception is distributed to all our workstations.  Keeping them in separate GPOs results in the exception for program B (but not all) not being applied to some of our computers.

"gpresult /H" shows both firewall exception GPOs being included, but the settings from the second GPO do not show up.

Any thoughts on why I would see such behavior?

John