### Fixes: #11582
Not sure if this is the correct fix or not. The reason that the custom field errors were not shown is that messages.html only shows non_field_errors if the form passed to the context is named form. This is probably an issue in more places, but not sure how to make it generic. A change to messages.html would also need to support formsets.
Any input appreciated @jeremystretch or @arthanson