Looking at the shard buildings, it seems to me that building an altar at an elemental shard gives +1 mana per turn and +1 shard power for the given element.

What puzzles me is the next item. Shard shrine description shows +2 mana, +1 power. I've always thought this would increase the bonus to a total of +2 mana and 1 shard power. I pretty much never build shrines in my games. But when I look at what the effect of the building is, shown in the lower area of the Build menu, it shows an increase of mana production from 1 to 3.

Is the +2 from a shrine cumulative with the +1 from the altar?

Surely this isn't so with other buildings like smelter, mason, etc.?