oboe,
The skin was submitted with P51BART1_a.bmp being all black. Checked the external view in the Training Arena as you suggested and the skin displays correctly – no default nose art.
Try changing your Max Texture Size – from AH2's startup page, select VIDEO SETUP, change Max Texture Size, and click OK. AH2 will then rework the skins and it might fix the problem. Go back to the TA and see if the nose art is still visible. If this fixes the problem, set your Max Texture Size back to what you had and see if the problem remains fixed.
HT should be redoing the 3D model or at least the UVW maps for the P51B some time. So I don't suspect this problem being very high on their priority list. Hopefully the cycling of the texture sizes will fix your problem.
MachNix