Do this: open thunar, then run a slow application, like FireFox. While FF is starting in the background, start resizing thunar window. FF will pop up, steal focus and won't let you continue resizing the window.
I use Xubuntu 11.10 i386.
Works for me:
I ran "sleep 5; xterm" while resizing and could continue resizing the window after the xterm appeared.
Ok, i see it does let you continue resizing, but the new window hides the one I resize.
I did "sleep 5; opera" (opens maximized) or "sleep 5; firefox".
Is it possible to keep showing the resized window in the foreground?