wxStaticBox with empty labels - wxMac compared to wxMSW

[Nusret Taşçı]

I'm using wxStaticBox with empty labels.
On wxMSW the staticbox looks like following:
+----------------+
|        [ ] cb1 |
| desc   [ ] cb2 |
|        [ ] cb3 |
+----------------+
There are several more UI elements. I didn't want to give the staticbox 
a label, because it would not look symmetric anymore.

On wxMAC it looks like
+----------------+
|                | <-- POI
|        [ ] cb1 |
| desc   [ ] cb2 |
|        [ ] cb3 |
+----------------+

It looks like there is one additional line calculated by the sizer.

If I use labels, than it looks like this on wxMSW:
+- label --------+
|        [ ] cb1 |
| desc   [ ] cb2 |
|        [ ] cb3 |
+----------------+

and on wxMAC it looks like this:

  label
+----------------+
|        [ ] cb1 |
| desc   [ ] cb2 |
|        [ ] cb3 |
+----------------+

So both look and behave fine if it has a non empty label.

Is this the intended behavior for Mac?
It's quite unhandy to change this behavior in my app, because the 
wxStaticBoxes are encapsulated by wxStaticBoxSizers in an XRC.