_changeform_view sends wrong object after ModelForm validation

[ddein]

I noticed strange behavior when changing the form of the admin. If I try to save the form with an error, some functions (get_fieldsets, get_prepopulated_fields, get_readonly_fields, get_inline_formsets, something else) get the wrong object after validation. See here: ​https://github.com/django/django/blob/master/django/contrib/admin/options.py#L1436-L1437
It seems to me not obvious, that after call is_valid, object obj will be changed. The quick solution for me was the following:

form = ModelForm(request.POST, request.FILES, instance=copy.copy(obj))

But maybe the problem elsewhere. Has anyone encountered a similar one, is this a mistake or normal behavior?

[Tim Graham]

I think this is related to this note ​in the documentation:

The cleaning process modifies the model instance passed to the ModelForm constructor in various ways. For instance, any date fields on the model are converted into actual date objects. Failed validation may leave the underlying model instance in an inconsistent state and therefore it’s not recommended to reuse it.

[ddein]

Replying to Tim Graham:

I think this is related to this note ​in the documentation:

Alright, I can check my code and not allow this error. But we are talking about the code that is used in administration and obviously a correction is needed here.