Uncleaned cyclic reference in python Routing lib

[Grenby]

What version of OR-Tools and what language are you using?
Version: 9.14.6206
Language: Python

Which solver are you using (e.g. CP-SAT, Routing Solver, GLOP, BOP, Gurobi)
Routing Solver

What operating system (Linux, Windows, ...) and version?
Linux

What did you do?
I use callback for each solution with link on RoutingModel to track the progress of the solution:

    callback = SolutionCallback(routing)
    routing.AddAtSolutionCallback(callback)

Where callback:

class SolutionCallback:
    def __del__(self):
        print("DELETE SolutionCallback")
    def __init__(self, routing: pywrapcp.RoutingModel):
        print("CREATE SolutionCallback")
        self.model = routing
    def __call__(self):
        pass

And in log console I see only "CREATE SolutionCallback".

Memory usage for example from official cite (https://developers.google.com/optimization/routing/vrp) with solution callback (I run it in loop 10_000 times):

I can remove this cyclic reference by:

callback.model = None

After that callback remove.

I didn't find that I need to nullified it in the documentation. I think it is unexpected behavior because by default python can remove cyclic reference.

What did you expect to see
Automatically remove circular references or make a new mention in the documentation that the dependency needs to be nullified