MC will freeze when copying a large file to a FAT drive. Can not be killed with pkill -9. umount will freeze trying to unmount the drive. There seems to be disk activity in gstat, so it might really be still copying the file.
But MC should normally just show the progress, not freeze till "when it's done"!
mount options for the FAT drive: msdosfs, local, noatime, noexec, nosuid
It does this independently of file system. I have just experienced the same hang on drive mounted "ufs, local, noatime, journaled soft-updates".