Originally Posted by NZLamb

Both of those MIMO cards use the same chipset (Atheros AR5005VL) and therefore the same driver. I'd suspect the issue is with the driver itself, try using a reference Atheros driver for both cards and see if that works.

There is a reference driver available at http://www.funchords.com/Atheros_4.1.2.71.zip although I don't know if it supports the AR5005VL.