Could it be that 6.0 only registers those controls listed using window class dependencies in the manifest file? If what you say about 5.82 is true your patch is correct though ofcourse.
I've checked both 5.82 and 6.0 (with a "standard" manifest) and both registers all the classes. I don't know if it's possible to list window classes dependancies in the manifest and how comctl 6.0 treats it. But as currenly we don't parse the manifest file we couldn't do anything with this.
Mikolaj Zalewski