This is a known issue and it has been fixed in version 6.5 which is now in beta. Currently, beta 1 is available on the site for download, but today we are going to make beta 2 available, which is very close to what final release will be.
Currently, we do not have any ETA of the Mac version, sorry for that. But it is our next priority right after we release an updated mobile client which is due this fall.
Do not hesitate to ask me if you have other questions.
We could use a remote session. E.g. connect to your Viewer PC for an attended remote session, and see what steps you perform when you try an RDP connection in the Viewer.