I had the same thing happen with two of my four map uploads. The first and fourth ones uploaded normally. For the second and third, instead of uploading normally, it said it was done instantly, then it was sync'ing my file with the file on the workshop. So if this is happening, you should be able to tell by looking at the icon on your task bar should have the dotted line showing sync’ing. Basically it was background uploading the files… (taking pretty similar time to how long it takes normally), and would pause the upload if I ran a game. While freaky, it did upload the files to the workshop. I also have no idea why this happened. I too would prefer if it just uploaded the file normally.