Username hint not being set on Windows 8.x

Since upgrading to Windows 8, and subsequently 8.1, RDM no longer updates my registry with the last username used for each server address. These values are found under HKCU\Software\Microsoft\Windows\Terminal Server Client\Servers. There is a subkey under there for each server address, containing a string value named UsernameHint.

On Windows 7 and older, RDM updated the username hint with the last credentials used to log into a server, but on Windows 8 and later, it reads the existing values from the registry, but does not create them when not present, nor update them when different credentials are used at the login screen. Credentials for the connections are not stored with the connections or in any repositories.

I ran Process Monitor and can see where it reads these values, but don't see any failed attempts to write back to the registry, so I'm not sure why this is happening. I'm wondering if it has something to with the updated RDP ActiveX control in Windows 8.x, as the username hints are updated properly when using the standalone mstsc.exe.

Can this be fixed or worked around somehow in RDM?