The reasoning is somewhat complex:

void Window::ImplInvalidateFrameRegion( const vcl::Region* pRegion, InvalidateFlags nFlags )

sets the mnPaintFlags on the mpWindowImpl - and then queues an idle
paint. This paint in LOK mode does ~nothing - since all rendering is
tiled, although amazingly it does emit eg. selection callbacks.

However the paint flag - changes the behavior of Window::Update() to
force a complete window invalidate. This happens, but only rarely -
when a key-event manages to get into the mainloop before the idle
paint handler arrives and does nothing (except clear the paint flags).

So - don't do these big invalidations we don't need to in lok mode,
unless it is for dialogs - which presumably Pranav wanted fixed by
625087b5.

Change-Id: I88dda34b8d8bba9c89296d883ad9169fe49a7c5e
Reviewed-on: https://gerrit.libreoffice.org/71395
Tested-by: Jenkins
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>