I have been playing around a lot with 2012 R2 RDS.
I was putting a demo together for a customer and I have a very odd problem. When logged in as a regular user the UI is very slow, when logged in as the administrator its fine.
What is strange is that if I play 720p video logged in as the user its perfect even in full screen so its not a bandwidth issue or connection issue.
Host server is Hyper V 2012 R2 Server, 2 guests, a demo DC and demo RDS server. RDS server has 2 cores, 4GB of ram. Just Office 2013 installed.
Very light GPO's, mostly hiding drives, drive mappings, shutting off the control panel, setting home page, etc. Desktop Experience is installed but it happened before/after.
Both from scratch just last night.
When you open an explorer window or go to the start menu its almost like slow motion, but video plays perfect. Even when you open up Office 2013 for the first time that animation plays smooth.
Client is my 8.1 Pro laptop so its using the latest RDP. If I use the Remote Desktop Manager which I believe still uses the 7.0 RDP stack its fine, only when using the RDP Client with the 8.1 protocol.
Done this a few times with no issues not sure what it is.