XLIB/DPMS:DPMS-DISABLE sometimes results in an asynchronous LENGTH-ERROR

[r13l]

It is difficult to reproduce, but this code will often (not always) result in a LENGTH-ERROR:

		(xlib/dpms:dpms-enable *display*)
		(xlib/dpms:dpms-set-timeouts *display* 900 1200 1800)
		(xlib:display-finish-output *display*)
		(sb-ext:process-wait (sb-ext:run-program "/usr/bin/slock" nil)
		(dbus:with-open-bus (bus (dbus:system-server-addresses))
		  (dbus:with-introspected-object (session bus *session-path* "org.freedesktop.login1")
		    (session "org.freedesktop.login1.Session" "SetIdleHint" nil)))
		(xlib/dpms:dpms-disable *display*)