Multiple Categories Selector removing categories added in custom handler.. bug ?

Hi,

I've noticed some unwanted behaviour when using the Multiple Categories Selector form control on one of my pages.

When I save (or intially create) the content page I have a custom event handler (on InsertAfter) that assigns some default categories (using DocumentCategoryInfoProvider.AddDocumentToCategory) based on another setting on the page (effectively copying the categories from another document). This part works fine.

However, after my handler has done this the Multiple Category Selector runs some code that effectively undo's this.. deleting my changes! The code in question is :

~\CMSModules\Categories\Controls\MultipleCategoriesSelector.ascx.cs

        // Remove old items
        string newValues = ValidationHelper.GetString(selectCategory.Value, null);
        string items = DataHelper.GetNewItemsInList(newValues, mCurrentValues);
        if (!String.IsNullOrEmpty(items))
        {
            string[] newItems = items.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
            // Add all new items to user
            foreach (string item in newItems)
            {
                int categoryId = ValidationHelper.GetInteger(item, 0);
                DocumentCategoryInfoProvider.RemoveDocumentFromCategory(Node.DocumentID, categoryId);
            }

            logUpdateTask = true;
        }

If i hide/remove the form control from my page type then everything works fine. Is this behaviour expected ? Is it a bug ? Is there a work around where I can still have the form control on the page ?

I understand that I can still manage/view the categories in the Category Property Page but having the form control provides a level of convenience.

V 9.0.12