Function definition with a call of a function using the same dummy identifier name

The following code works

f1(x) = (f2(4) + x)
f2(y) = 2*y
print(f1(2)) # 10

but this does not:

f1(x) = (f2(4) + x)
f2(x) = 2*x

I get this error:

Traceback (most recent call last):
  File "../scripts/run_model.py", line 19, in <module>
    program = meta.model_from_file(model_file)
  File "/home/ubuntu/python3-venv/lib/python3.8/site-packages/textx/metamodel.py", line 634, in model_from_file
    return self.internal_model_from_file(
  File "/home/ubuntu/python3-venv/lib/python3.8/site-packages/textx/metamodel.py", line 688, in internal_model_from_file
    p(model, self)
  File "/home/ubuntu/vre-language/constraints/functions.py", line 61, in check_functions_processor
    check_function_definition(func, metamodel)
  File "/home/ubuntu/vre-language/constraints/functions.py", line 29, in check_function_definition
    assert not any(d in args_uniq_names for d in call_dummies)
AssertionError
"""

It is not just because of the same dummy names because it works without a function call in the function definition:

fx1(x) = 1 + x
fx2(x) = 2*x
print(fx1(2)) # 3

There is a test catching the issue. When the issue is solved the test will fail.