That the glass material is reflective is stated in the Reference Manual:

Glass is similar to dielectric, but it is optimized for thin glass surfaces (n = 1.52). One transmitted ray and one reflected ray is produced.

Since this is a perfect abstract material, I expect the reflectance to be (1 - T), where T is transmittance. the transmittance). The details are in the code in glass.c.

(Hey, Unmet Hours, how 'bout support for equations?)

That the glass material is reflective is stated in the Reference Manual:

Glass is similar to dielectric, but it is optimized for thin glass surfaces (n = 1.52). One transmitted ray and one reflected ray is produced.

Since this is a perfect abstract material, I expect the reflectance to be (1 - the transmittance). The details are in the code in glass.c.