My problem originated on a misconception of the functionality of the repetition rule in combination with entry criteria. So there is no longer a problem with camunda in this regard.
However, there seems to be problem with the timing of variable evaluations, when the entry criteria has no connection/on-condition. Something like this:
I would be expecting a infinite loop, when both entry and repetition rule evaluate to true. Instead the newly instantiated task becomes only then active, when an arbitrary variable get changed/added.
I am not sure to what extend this behaviour is intended or if is is a limitation of the engine.
Just my 2 cents, as i have found a solution for my original problem.