FWIW, the multi-instance Properties view code had a hook to close all
secondary Properties views on window close (saveState() was called on
window close only). With the auto-save functionality added later,
saveState() is now called also on auto-save intervals, causing the
secondary Properties views to be closed during normal work, which is
highly surprising to the users.

Keep the old behavior to close secondary Properties view instances on
window close, but avoid closing them automatically in saveState()
otherwise.

Change-Id: Id7eeaf44fa1b169df47801ee5be8ec3dd75fc62f
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>