PaulS:
Sometimes I have to do it three or 4 times to get the copy to happen.
I use various forms of remote desktop and VM hosting applications and remote terminals and so on that support clipboard integration. I will routinely be connected to a dozen different systems with a shared clipboard. Which is absolutely excellent when it works and saves a load of work. But sometimes my system seems to get itself into a state where some copy operations simply don't do anything. My guess is that somewhere in this mess of clipboard syncing the copy is getting lost or 'undone'. This causes similar symptoms where a single copy will often fail but repeated copy operations will usually work. Ringing any bells with your situation?