Here is an interesting one.

A USB key is accessed and it already has some content. If I try to move a directory on top of it, so to update the content on the USB key with fresh data from my PC, it says there is not enough room. If I clean it up before doing the operation, it works.

And, this is not only the differential, there was enough space on disk. But, it seems the calculation of the available disk space is calculating on top of the existant data and not detecting that some files are already there and only see about the difference.

I would assume that might be normal as it allows a faster detection on potential disk space. On the opposite, a calculation on file to file approach would take longer.

Does anyone know if this is specific to that particular concept of if this is Windows based in general?