Hello Gernot!
The bug is box to box, box to poly, poly to poly,
The only thing that works is circle to everything else including circle to circle.
Did you read the post in the box2d forum??
That guy had exactly the same problem, under windows run ok but have that bug on the iphone...
Finally he found the problem and solution:
"The ClipVertex objects were not created properly in the engine because of a small change I made. Peculiar how it worked on Visual Studio though. I guess some difference in the compilers..."
I don't understand nothing about ClipVertex objects and how GLbasic is handling

but I guess that there is the problem, maybe you need to change something ...
Gernot, we believe in you!

Bye!