NOT A BUG

@AndrewGarrison Ok I'll do it.

The solar panels are colliding with the fuel tank. This is working as expected. You can try disabling collisions for the solar panels in the Tinker Panel by setting Part Collisions to Never.

@Klosskopf Yeah, I used big solar panels, but not the extendable ones.

Does it still happen after increasing the hinge strength?
I once had the same problem, but could "solve" it by using less heavy solar panels, so I thought it was about the hinge strenght