I wonder if you're running into any bugs with the current release v3.71.78 AWUSB driver. Might want to try rolling back to the previous version, 3.60.60, to see if that helps. Uninstall the current driver through Programs and Features, reboot the computer, then install 3.60.60. Does any of the behavior change?
3.60.60 32-bit: http://ftp1.digi.com/support/driver/40002670_L.exe
3.60.60 64-bit: http://ftp1.digi.com/support/driver/40002668_L.exe