Rich text field not accessible in derived template

[Enigma]

Hello,

I already created some derived templates that included small forms, and they always included the rich text field from the Text template they were derived from.

Now I created a template that uses a more sophisticated form with about 40 new attributes. During the creation, I always added some attributes to the form, then saved (by clicking "OK" and "Close"), and for quite a long time the rich text field was visible below the form. Near the end of the form creation process it suddenly disappeared. The Primary Attribute is still "Rich Text" though.

Is this a feature that only occurs when a form exceeds a defined size, or did I make a mistake? Or is it a bug? Is there a way to get the field back?

I added screenshots of the final form definition and of the item attributes of the template.

Cheers,
Jan