If a form is in "Design mode OFF" (live-mode), the form controls are windows and as such they are always automatically in front of other content of the page. To mimic this behavior in design mode, the layer "Controls" was invented. Objects on this layer are always in front of objects in other layers and form controls are always automatically assigned to this layer.
Reasons for removing it:
* A novice user will not understand, why this layer exists.
* If a normal user is experienced enough to use layers, he will not understand why objects on this layer are excluded from arrangement (=z-order), even if they are not form controls but simple shapes.
* Removing this layer simplifies the UI.
* Removing this layer simplifies the code. Current behavior produces a lot of special cases in the code.
* The file format has no means to store, that "Controls" is a special layer.
* On import of foreign documents this layer is automatically inserted, although not contained in the original document.
Why it is no large loss:
No wizard produces a form as Draw-document, only text documents and spreadsheets are used by wizards. So only users experienced in data bases _and_ Draw will create a form as Draw-document. Such users can be expected to use the arrangement tools to keep design-mode and live-mode visually equal. For such users an additional command "Bring all form controls to front" would be enough, if it is desired to give them a tool for quick adaptation. The visible/printable/protected properties of this layer are available with ordinary layers too.
IMHO agree the Controls layer can go... "Bring all form controls to front" would be enough.