Quoting Toni Cebrián
When I do the xprop in that strip, I get: <snip> Perhaps de nautilus --no-desktop is not working as expected?
Well, the output you posted didn't set any struts at all. While I can't be 100% sure, it seems whatever window you happened to click on was not the culprit causing the blank space along the right-hand side. Try clicking a few other windows; you're looking for a property labeled "_NET_WM_STRUT_PARTIAL(CARDINAL)". To double-check that it is indeed a rogue strut, you can take "avoidStruts" out of your xmonad.hs temporarily; if the space goes away after a reload (and possibly a layout ping, by default bound to mod+shift+space), then some window is setting a bad strut. This would make me 100% sure that the nautilus window you clicked is not the culprit. ~d