In material parsing, the post-compiler fails to parse materials whose names contain the ".vmt" extension

[long0900]

A VMT can reference another VMT by using a file name with .vmt extension apparently.
For example, in tf2_misc.vpk/materials/water/water_underworld.vmt:
"$bottommaterial" "water/water_underworld_beneath.vmt"

The post-compiler will fail to get the correct material because it append the .vmt extension to the material again, which already exists.
[WARNING] packlist._get_material_files(): File "materials/water/water_underworld_beneath.vmt.vmt" does not exist!

[long0900]

This might also happen with texture files