I have been working alot with two plugins that relate to and affect categories in WordPress. However these plugins did not play nice with eachother at first and I decided to find out why.
After alot of code reading I found that the reason they weren't working well together is because the edit_category_form-hook occurs AFTER the submit button for the edit/add category-forms and they both want to be BEFORE the submit button of course.
All that needs to be done is to move the hook to before the table is closed in edit-category-form.php and moving it up above the p-tag with the class submit in categories.php.
If there's a special reason that the hook must be placed after the submit button there should be another hook for those who want to add form fields to the category forms.