Nick, we are not able to repro this issue.Steve Lee commented
Nick, I'm not able to repro this on Win8.1 manually upgraded to WMF5 RTM. I'm not sure what you mean by "deploy WMF 5.0 RTM to Windows 8.1 Industry Pro thru WSMan". Perhaps if you can provide a bit more repro steps I can figure out what the problem is.
For now, you can get back to a good working state by running "enable-psremoting -force" from an elevated PowerShell prompt.