It's not executing, or calculating, on any drive. It's doing that in RAM. It could be that Windows is using a drive other than C for paging virtual memory. Remember that free space is never truly accurately reported because of both paging memory to disk and, if you have your machine set to hibernate, reserving of space to record a map of current machine image for resuming.

It's also possible that Vue makes temporary files on the drive from which certain resources are loaded. It was the bain of my life for years that my users kept opening MS Word documents from floppies which, prior to Office XP, resulted in Word creating a temporary file, in which it recorded all changes - complete with times, author etc - on a drive without sufficient space!

It could also just be that your F drive is very slow.