Not a bug report but a crucially missing setting:
The hole fill tool (Modeling->Triangles->HoleFill) always assigns the first (Element 0) material to the newly formed triangles. A quick override setting that would allow to pick which of the mesh’s existing materials to use would greatly improve the tool’s workflow.
(There’s already a Material Node Override setting in the Transform UV tool (UVs/Normals->Transform UVs), but it’s only used for previewing the UV layout and doesn’t apply the material to the selection.)