When using RDP, you want to let them be redirected using the built-in HID redirection, do not redirect them as USB devices. In fact, if you only need the pasting of barcodes and don't have software that needs more advanced functionality, this should be sufficient for PCoIP also.
Assume for a second they are identical to a keyboard (when pasting barcodes they're essentially just typing the number), if you RDP to a remote physical machine, the RDP session is kept separate from the console so that local keyboard usage doesn't interfere with your remote session. The device will be working, but the output won't be going into your RDP session. PCoIP is a console remoting protocol (think VNC but much better), so it's as if you're sitting in front of the physical machine and the "keyboard" data will be going to the correct session.
Hope that helps explain what you're seeing.
Mike
