What happened?

0. In my plugin I have a Model that extends com_content/CategoryModel which builds on AdminModel and FormModel.
1. When I call in my getForm() the $this->loadForm('componentName.category', category) everything works as expected.
2. When I call $this->loadForm('componentName.category', 'category_some_specific_variant') I don't get the fields from category_some_specific_variant.xml but the ones from category.xml
3. Digging deeper revealed Form->loadForm() from the FormBehaviorTrait calls $this->preprocessForm.
4. The preprocessForm from com_content/CategoryModel calls $form->load($addform, false)
5. The Implementation of Form->load() is supposed to remove a field from the data if it is already present in the form and $replace == false.
6. Line 659 unset($field); is wrong for SimpleXMLElement, this only removes the local variable without removing the Element from the data tree.
7. According to https://www.w3docs.com/snippets/php/remove-a-child-with-a-specific-attribute-in-simplexml-for-php.html correct removal code would be unset($field[0]);

Version

6.0

Expected result

both xml files category.xml and category_some_specific_variant.xml exist and
I call $result = $this->loadForm('componentName.category', 'category_some_specific_variant')
I expect $result->getXML to contain only one fieldset with correct overwriting, with category_some_specific_variant.xml taking precedence over category.xml

Actual result

System Information

Joomla! 6.0.3 Stable [ Kuimarisha ] 17-February-2026 16:00 UTC
PHP 8.3.16

Additional Comments

The issue applies to all current Joomla Versions afaik