Just out of interest - is this always copying from a Metro app to somewhere else (i.e. doesn't affect Desktop?)

I'm wondering whether this might be related to the auto-hibernation of background Metro apps - lots of clipboard actions are managed by COM and Windows messages under the hood, so if you copy something onto the clipboard which actually sets the OleClipboard to an IStream, you might find that you're unable to get the data out at the other side if the program has suspended.

Sounds like an avenue for investigation at least... :/