Unwanted panels in Notes Designer

I have accidentally added three additional panels to my Notes 8.5.3 Designer client. The panels are empty (i.e. blank grey) apart from a minimise/maximise icon. I don’t know what they represent or how to get rid of them, but they are taking up valuable screen space. Started with just one, but when I tried to drag it off the screen it duplicated - and that happened once more. I just want my standard Designer panels back for plain vanilla non-web development (list of applications, selected design elements, properties) so how can I close these unwanted panels? What are they? Why don’t they show up on the menu as something-or-other ticked, so that I can untick every panel I don’t actually need?

Subject: Change perspective

Window, Open perspective, Domino Designer (or Forms/Views)

Subject: I tried that

Thanks for your suggestion, Karl-Henry. It would seem the logical thing to do (either that or return to default perspective) and I had already tried both options, but the empty grey panels just won’t disappear. They have no title, no icon to close them - nothing. Even the single icon that they do have (the maximise icon) no longer works. I can maximise and minimise any one of the grey panels by double-clicking on it, but nothing will make it go away. I’m afraid I might have to reinstall Notes from scratch. I just can’t understand how such a glaring design fault could exist.

Subject: Even worse

Then I tried the ‘Close All Perspectives’ option, thinking I might then be able to selectively open the panels I want. But there is no longer an option to open any perspective whatsoever. I’ve got nothing, so I give up: I’ll just have to reinstall.

Subject: Finally some joy …

After closing all perspectives, I rebooted my PC and relaunched Notes + Designer. The default Designer panels have been reinstated. At least I’ll know what to do if I ever inadvertently create extra empty panels again, but it would still be good to know how empty panels get created (what exactly are they?) and whether there is an easier way to get rid of them.