That is not the case on win 8 pro x64 and never has been
There is a complexity of tools exe's starting viewers and second line exe's that simply allowing p drive to bypass UAC does not fix , pdrive as you know is only a subst , creating it does not then allow uac to be bypassed on the exe's contained within .
For example start steam as user then mount p , then start TB and launch bulldozer annd you will recieve viewer not found .
However if you start steam as admin then do the same all will be ok ,
however as a user you will not physically see the p: drive as a drive label because your a user not admin .therefore you have to go direct to the armawork folder or go via the open file in the tool UI.
I have started p drive via the bat as both user and admin since day 1 and still do if I do it through tools ui it will only show to the authority that started the steam exe .