Pycharm 2019.2.5: debug console not updating variables / state for declared variables

When stopped at a breakpoint, executing commands in the console doesn't update the state in expected ways, or update the state inconsistently.

Example script:

def f():
    a = 1
    b = 2

f()

when debugging this script and stopping at a breakpoint at "b = ..." line (before it's execution):

1. If I execute `b=2` in the console (interactively) and immediately after that I execute `print(b)` I get "NameError: name 'b' is not defined". Even though I've just assigned it.

2, If I execute `c=3` in the console and after that `print(c)` I get the expected "3".

3. If I execute `a=10` in the console, and after that `print(a)` I get "1", despite updating the variable interactively.

It seems that for some reason, variables that are declared in the scope of the breakpoint cannot be created / updated interactively in the console.

What may be the reason for this strange behavior? I'm running Pycharm 2019.2.5 (with python 3.6).