During last weekend I've spent some times around wireless support and I've discovered a bug.
I've already fixed it and I can post here that the DWA-140 problem you mention is part of the bug.
To solve it prior to the next image you should connect via telnet or SSH to your box and issue a simple command:
Code:
opkg remove kernel-module-rt2800usb --force-depends
In the next Image (or Revision) the rt2800usb driver will be drammatically reduced and reconfigured to be invoked only with specified devices and not for other wifi sticks governed by chipset vendor driver that are included into BH images.
I've tested the above command with my Vu+Uno and a DWA-140 B2 FW 1.31.
Initially the device will be detected as rt2800usb device and doesen't work properly (variable speed and other problems with my wireless router)
After launch the command, I've reconfigured my box and now my DWA device works as expected (270Mbit/s) and uses the properly driver.
I would like to remember that this modification will be included in the next Image / Revision.