Active comparator doesn't give off light / unused comparator block

A deactivated comparator does not produce any light, as expected. (Picture 1)
However, an activated comparator does not glow either. (Picture 2)
Instead there is an unused activated comparator (ID 150), which does give off light. (Picture 3)
If this unused comparator is depowered and activated again, it turns into a regular not-glowing comparator. (Picture 4)