It is a new connection (end of one, start of another), not just a change in the screen resolution. And they are not capturing and saving credentials to logon on your behalf (I don't think you would want that).
The 'basic' connection uses the VMConnect.exe application and proxies the console of the VM.
The 'enhanced' session uses the RDP client (and still proxies the connection).
A third possibility is to use the RDP client and connect directly to the RDP listener of the VM (assuming windows in the VM) and avoid the proxied connection all together.