Hi Arturo,
You were using a Quarter Klems-basis BSDF for the glazing. That could be one of the issues. There is no practical reason to use BSDFs to represent purely specular glazing unless there is some multi-phase calculation invovled. Glass material typically gets stored as a diagonal matrix in the BSDF format (first image below).
The calculation that you are performing is represented by the first row of images, where the rays are directly traced to the sun and sky. BSDFs for purely specular glazing, if used, are required for Three Phase Method and beyond (row 2 and row 3 in the image below).
Detailed info, and links to further reading material, can be found in Chapter 2 of the tutorial from which the above images was taken link.
Regards,
Sarith