This patch seems to have fixed the strange problem with the _N map, however there is a problem with the specularity map (I don't know if this problem was also present before or if its new). If I create a custom skin folder and copy into it only the diffuse map (base skin), the normal map (_N.bmp) and the specularity map (_S.bmp), the specularity is not the same when comparing the skins. In the screenshots below, you can tell the anti-glare painted areas are too reflective on the custom skins. The last screenshot I used a _S.bmp file with nothing but pure black (x'000000') and the skin still shines. It is even more noticeable on the default P-38J, since the whole aircraft is painted with flat paint.

Also, it appears that the DX11 version does not support the "Save Default Skin" function inthe hangar menu. I tried saving the C202 default skin in DX11 and it creates an empty c202 folder. I deleted it and restarted the DX9 version, saved the default skin and the c202 folder is there with all the proper contents.
EDIT: Just confirmed that this skin specularity bug occurs in both DX9 and DX11 versions.