Okay, the kickstand is loose for quite a while. So it was broken for a long time.

So have you never thrown your phone against are wall or so ^^? Me neither, but one day in winter, when the streets were icy, I was out for geocaching. I was using the N900 as a GPS device. I looked on the N900 and didn't recognize the ice. So I slipped, the N900 fell off my hand and flew about 5 meters and dumped on the ground and slithered another 5 meters. I only recognized some tiny scratches (bought a Zagg shield after that event ). Maybe that was the time when kickstand spring got cracked.

And the black blob belongs to the spring I guess, as on the other pictures there are these black blobs on the spring.

If I would not have forgotten the spring at work, I would do some repair actions mentioned in the other thread. Thanks for all your help.

And the spring is not that important to order a new back cover.