I have two mirror hosts with scripts to backup each other. My problem occurs as trivial race condition beetwen backup scripts and X11 forwarded thunar sessions.

I tried to copy file between two thunar instances on two hosts. As I wrote I have two mirror hosts so problem looked like this:
- changes to file a.txt on host A
- select and copy via thunar a.txt on host A
- paste via thunar on host B file a.txt to a up one level directory
- result was older file from host B copied to up one level directory on host B
- and then mirror scripts fired up and I have on two hosts two versions of a.txt older and newer

Sometimes that could lead to corruptions of files in some conditions, because paste command from thunar on host A issues command on host B like.

cp src/file dst/file 

where src/file and dst/file are on host B. 

I think copy-paste, cut-paste possibility should be prevented between two X11 forwarded instances, but that shouldn't cause problems to clipboard copy,cut,paste.
I think that's not only Xfce-thunar problem but other file managers too.