Light source stacking

It seems that all light sources that are placed into a primary inventory slot do overwrite the light effect of equipped light sources even when the ligth of those is brighter. Stacking does work correctly when different light sources are equipped and none is in a primary inventory slot.

Example:
Summoned: Light Globe - Primary inventory slot - Weak light - This light is active
Summoned: Halo of Light - Equipped on head slot - Bright light

Summoned: Light Globe - Equipped on primary hand slot - Weak light
Summoned: Halo of Light - Equipped on head slot - Bright light - This light is active

Is it the same light in both because Light Globe should be brighter

Halo of Light is much brigher and a higher level spell than Light Globe.

Level doesn't matter, Light Globe should have a light source of 9 and Halo of Light should have a light source of 7, believe higher is stronger/brighter