PS, the images on my post have been removed for some reason. You can see the 2 images I posted here:

http://i.imgur.com/b7sdu3e.jpg

http://i.imgur.com/6gqgbFl.jpg

Hello Simon 

Can you post of an example of the code you are using to get this behaviour?

David

My editor descriptor looks like the following. Note that there is some other code in here that a) sets the root category for the category picker b) Sets the visibility of the category picker based on the page type. Essentially, there is just one line that sets the tab (metadata.GroupName = Tabs.Topics;)

[EditorDescriptorRegistration(TargetType = typeof(CategoryList), EditorDescriptorBehavior = EditorDescriptorBehavior.ExtendBase)]
    public class TopicsEditorDescriptor : EditorDescriptor
    {
        public TopicsEditorDescriptor()
        {
            EditorConfiguration["root"] = CategoryHelper.GetTopicsRootCategory().ID;
        }

        public override void ModifyMetadata(
           ExtendedMetadata metadata,
           IEnumerable attributes)
        {
            base.ModifyMetadata(metadata, attributes);

            if (!String.Equals(metadata.PropertyName, "icategorizable_category"))
            {
                return;
            }

            dynamic dynamicMetadata = metadata;
            var ownerContent = dynamicMetadata.OwnerContent;

            if (ownerContent is RsaBasePageType && ((RsaBasePageType)ownerContent).CanTag)
            {
                metadata.ShowForEdit = true;
                metadata.GroupName = Tabs.Topics;
            }
            else
            {
                metadata.ShowForEdit = false;
            }
        }
    }

I also have an inititialization module that organises my tabs at app start-up, although I'm not sure if this is relevant. My code for that module is similar to the solution posted here : http://world.episerver.com/Forum/Developer-forum/EPiServer-7-Preview/Thread-Container/2012/10/Tabs-and-sort-index/

BTW, the inspiration for this editor descriptor was taken from here:

http://world.episerver.com/Blogs/Linus-Ekstrom/Dates/2013/12/Custom-root-for-category-selection-and-EditorDescriptorBehavior/

and also here:

http://joelabrahamsson.com/hiding-episervers-standard-category-property/

I did some more playing around with this and it does seem that this is a bug that occurs when there are no regular properties and the category picker is the only thing present on the tab. 

If I add another property to the tab, the tab displays correctly. I can even set this new property so that it is hidden in edit mode, and the tab will still render correctly!

This will be my work around for the time being unless it gets fixed (I'm guessing this is a low priority bug in the scheme of things).

Hello Simon, I am glad you got this resolved! If you haven't already please report this as a bug, so we have a record of it.

David