Fixed #19423 -- Prevented ModelAdmin sharing widgets due to formfield_overrides

Thanks joebuyer at manycycles.com for the report and Simon Charette
for the review.

1 files changed, 2 insertions, 1 deletions

diff --git a/django/contrib/admin/options.py b/django/contrib/admin/options.py
index c48ffa6ca3..f4c27511d3 100644
--- a/django/contrib/admin/options.py
+++ b/django/contrib/admin/options.py
@@ -1,3 +1,4 @@
+import copy
 from functools import update_wrapper, partial
 import warnings
 
@@ -130,7 +131,7 @@ class BaseModelAdmin(six.with_metaclass(forms.MediaDefiningClass)):
         # passed to formfield_for_dbfield override the defaults.
         for klass in db_field.__class__.mro():
             if klass in self.formfield_overrides:
-                kwargs = dict(self.formfield_overrides[klass], **kwargs)
+                kwargs = dict(copy.deepcopy(self.formfield_overrides[klass]), **kwargs)
                 return db_field.formfield(**kwargs)
 
         # For any other type of field, just call its formfield() method.