Form with ModelChoiceField and disabled failed when the initial is model instance.

[Eran Keydar]

Got this issue in some more complex example, narrows down to this scenario:

class Form1(forms.Form):
    user = forms.ModelChoiceField(
        queryset=get_user_model().objects.all(),
        disabled=True,
        initial=get_user_model().objects.get(pk=1)
    )
    label = forms.CharField()

Then

In [12]: f = Form1(data={'label':'aaa'})                                        

In [13]: f.is_valid()                                                           
Out[13]: False

In [14]: f.errors                                                               
Out[14]: {'user': ['Select a valid choice. That choice is not one of the available choices.']}

If the initial changed to the pk itself, everything works fine

[Mariusz Felisiak]

Duplicate of #30014. This is fixed in Django 3.0.