I just ran into this problem in Windows/OSX as well. I am syncing a file where the full path is 250 chars. If you add on the .!sync extension for the temp file you get to the magic 256 length and the file just syncs over and over again. It is only a 1MB file. I tried closing sync and manually syncing the file in both locations and then starting up, but it seems to puke on that length of file name. When I shorten the name everything works fine.