override_config stores the same dict object for every parameter that does not already have an entry:

if id(p) in self.pid2config:
    self.pid2config[id(p)].update(key_value_dict)
else:
    self.pid2config[id(p)] = key_value_dict

So a later single-parameter override takes the update branch and writes into the config every parameter from the earlier call is pointing at:

mng.override_config([p1, p2], "optim_bits", 32)
mng.pid2config[id(p1)] is mng.pid2config[id(p2)]   # True

mng.override_config(p1, "lr", 0.01)
# p1: {'optim_bits': 32, 'lr': 0.01}
# p2: {'optim_bits': 32, 'lr': 0.01}   <- never asked for

The docstring's own example is exactly this shape — register several parameters, then override one of them — so it is the documented usage rather than an edge case. Nothing raises; the affected parameters just train with hyperparameters the caller did not choose.

The same reference is handed back out when the caller passes key_value_dict themselves, so their dictionary grows behind their back:

d = {"optim_bits": 8}
mng.override_config(p3, key_value_dict=d)
mng.override_config(p3, "lr", 0.5)
# d -> {'optim_bits': 8, 'lr': 0.5}

The change

Copy on insert (dict(key_value_dict)). After:

p1: {'optim_bits': 32, 'lr': 0.01}
p2: {'optim_bits': 32}
d : {'optim_bits': 8}

The update branch is unchanged, so accumulating several overrides onto one parameter still works the way it does today.

Tests

Two added next to test_override_config_after_register in tests/test_optim.py, both CPU-only:

• test_override_config_does_not_share_one_dict_across_parameters — asserts the two configs are distinct objects and that overriding p1 leaves p2 alone
• test_override_config_does_not_mutate_the_callers_dict — asserts the caller's dict is unchanged while the stored config still accumulates

Reverting only optimizer.py:

tests/test_optim.py::test_override_config_does_not_share_one_dict_across_parameters FAILED
tests/test_optim.py::test_override_config_does_not_mutate_the_callers_dict FAILED
2 failed

and with the change, 2 passed. ruff check and ruff format --check clean.

Separate from #2028, which is in utils.py; no overlapping hunks.