Passthrough auth to vS from PowerCLI 5.0.1

I'm trying to get passthrough auth (i.e. equivalent of "Use Windows session credentials") to work to a vS (5.0) host from PowerCLI 5.0.1. From the VI client all is good (I can connect to the vS host by ticking the "Use Windows session credentials" box) however when I do a "connect-viserver -Server vSservername" from PowerCLI I get an authentication pop-up asking for credentials. If I try the same thing against a vC (5.0) then passthrough works correctly.

I've tried this with both 5.0.0 and 5.0.1, 64 bit and 32 bit PowerCLI. Any suggestions appreciated!