I wonder why, when copying large files to a memory, although the window with the progress bar is closed, the memory drive, I have to wait to finish copying the files, so that takes Dismount.
That does not happen with Gnome, for example, that when you finish copying the files, you can eject the memory immediately.
I have noticed the same thing. I think the file being copied shows as finished once the copied file is in memory. So the dialog box closes, but the drive is still writing. As long as you use the unmount command and just don't pluck the drive out, you shouldn't have any write issues.
I had the same issue in kde writing to flash drives. Setting to syncranous from asyncranous transfer took care of the issue there. Not sure where to set that in xfce4 if there is such an option though.