Just to clarify, the Removeable Flaw does show up in the Flaws if added as a Flaw. It's only the drop-down menu that doesn't get moved over. I don't have access to the source code, but using the debug windows, it's because the Flaw adds a
Gizmo, as all of the Extras and Flaws do, while the menu entry only adds a
Tag. Tags are an internal structure, and therefore don't get exported. You have to explicitly turn them into something that is exported.
Unfortunately, that's not something that can be modified in the Editor. It would need to be changed in the Authoring Kit files, which are not publicly available (since it has the entire game system).