.Net 4.5 comes with Powershell 3.0 which seems to break Sharepoint 2010 Powershell administration. That is because PSH 3.0 loads CLR 4.5 and SP2010 needs CLR 3.5 (AKA 2.0).
Add -version 2.0 parameter when executing Powershell 3.0, and Sharepoint integration should work.