Remote Desktop Web Access and windows key combinations

We use 'Server Type' = 'Remote Desktop Web Access'. 

So there is an HTTPS connection to the RDP server and this opens a new RDP connection to the end server as the user is prompted to enter the hostname.

In the 'Custom Parameters', it is included 'keyboardhook:i:2' whis is echoed back to the .rdp file - that's Ok. However, the Windows Key combinations that usually works in our computers, don't work there.