How does AUFS work when we delete a file and remount it into the union?
 

I'm using Porteus, which uses AUFS filesystem to mount modules into the union on the fly. I noticed that if I delete a file from the union (e.g /usr/bin/xfce4-taskmanager) it appears in /mnt/live/memory/changes/usr/bin as .wh.xfce4-taskmanager with zero byte. So far so good. However, if I try to mount a module with the same file/path, it doesn't appear in the union. Somehow the whiteout file has a higher priority in the stack. If I delete the whiteout file, then the real file (/usr/bin/xfce4-taskmanager) will automatically appear in the union. Also, if I manually copy (instead of mounting) the real file to the union, it appears normally and can be executed without any problem.

1- Is this the expected behavior?
2- Is there a way to set the whiteout files to have the lowest priority in the stack so that mounting files into the union will make them appear for the user?