Changing visibility of items (i.e. the pin box / deauthorise button)
whilst painting the ClientBox can cause extra Paint request to be fired,
essentially resulting in an infinite loop (although slightly slowed
down by going through a VCL timer). These repeated paints (and repeated
hide/showing) of items resulted in a rather ugly flickering, which
is now gone.

Change-Id: Ib6b22dd1b08f3be5d1f543cfbb27a1ed782b5720