ID 422984 - Shaders are not compiling the specular map correctly

Problem summary

Shaders are not compiling the specular map correctly

Customer reported version
mari_4.6v2

Steps to reproduce

1. Open the example material project 

result: Notice that the silver metal parts are displaying black instead of silver 

Expected behaviour
Mari should display the specular map correctly.

Actual behaviour
It shows as black.

Workaround
Unknown. 

Reproduced by Manual QA

4.6v2 MacOS 10.15, Windows 10, CentOS 7