As of recent changes to xmonad.hs (importing and using MouseResizeableTile layout and FindEmptyWorkspace action) xmonad --recompile's fine and if I log out and in again all is well, but if I issue an xmonad --restart nothing seems to happen. Certainly, my starthook is not run. As this behaviour is so totally unexpected I'm not sure where to begin to look. I have rolled back changes to the last time it worked, but to no avail.
darcs version 0.12 on ubuntu 14.04
This is a known problem when the workspace stack is too complicated to pass on to the newly spawned instance of xmonad - i.e. the arg list to the new instance exceeds the limits of the kernel. The failed instance falls back safely to the current running session.
Next question, how to increase the maximum argument length...