[wxMac 2.7] Art provider does not return icons of correct size

[H]

When trying to get an icon or bitmap using art provider I do not get the 
icons with the correct (default) size. Example:

wxArtProvider.GetBitmap/Icon(wxART_ERROR,wxART_MESSAGE_BOX)

I expect to get a bitmap or icon of size 64 x 64 (see Apple human 
interface guidelines). But I get a 32 x 32 icon (see also art provider 
sample).
When specifying the additional parameter wxSize(64,64) I get an 
interpolated icon of size 64 x 64. This is correct but as it is 
interpolated the icon looks pretty ugly.

Is this the intended behaviour of the art provider or a feature?

Hartwig