The Frostblood Proto-Wrym and Obsidian Worldbreaker mounts being flagged as grounds mounts isn't a bug or an error on the developers' part - it's because, as mentioned previously, these are promotional mounts designed to be used at both max level and lower levels (including where people cannot fly), so they're flagged in such a way that they'll pop up in both scenarios. The same is true of all promotional mounts, really.
That you find it annoying or aesthetically displeasing isn't a problem on Blizzard's part - it's a you thing, and if you *require* it to be addressed in order to be happy then there are approaches that will work, such as the aforementioned add-ons.