I did an experiment and it turns out that the files get split up even if it wasn't done all the moving...
Here's why I actually made the thread (should have made a better title....) I was trying to copy Folder A from hdd1 to hdd2.
As I said, I mistakenly moved the folder and hit cancel about 10% of the way through, resulting in Folder B on hdd2. I should have just let it go and copied it back, lesson learned.... :/
I then copied what was left in Folder A to hdd2 resulting in Folder C.
I then merged Folder B and C, thinking the files that made it through (when I accidentally moved instead of copied) got moved and there'd be no overlap. There were no duplicates so it seemed I was correct.
I checked the total size of the merged folders and it was the exact same as Folder A. This makes no sense. If the files in Folder B got moved (which should have been the case), then Folder A should have less data then B and C combined.
I've thought about this for hours, and the only explanation I can think of is that maybe I copied the contents of Folder B back to hdd1 BEFORE I merged B and C but AFTER I copied A to C. I can't imagine I'd forget doing that, but I was kind of in a panic at the time...
Is there another explanation I just can't think of? I double checked all the folders and I don't think my story is wrong...
Of course, if you need better explaining, don't hesitate to ask!