As a followup question, is this actually an issue? Does it cause problems with certain other Premiere Pro APIs that actually use the path?
Or was it simply unexpected (as it really does look like a bug when you first see it...)?
I think the APIs is not entirely consequential in its design; I haven't done a reverse test (feeding a "\\?\D:\path\to\file.ext" to a method which expects a "D:\path\to\file.ext" string), but I guess under the hood there are some error catching methods which add Win32-required prefixes or directives to the input. In other cases, read methods seem to return the Win32 result. Or maybe it's added there as well, I don't know... anyway, the results vary.
Right, I guess the question was whether the OP was experiencing problems when passing such a path to another panel API or not. If so, then it would be worthwhile to report it to Adobe.
On the other hand, they may simply need to special-case their logic if, for example, they're doing something with regular expressions or showing the path to users...