Bug: MatchSrf second picked surface stays visible in preview

@pascal

Matchsrf is not working as it should:

Hi Gijs - that is just the ‘Average surfaces’ setting at work here, right? I guess I see what you mean - with Average that second surface should go away.

RH-62884 MatchSrf - do not display either input when Average surfaces

-Pascal

yes, strange that I never was annoyed by this before but apparently it has been like that also on windows since v6. In v5 both surfaces stay visible. I think removing them from the view makes more sense