By placing a hopper on the ground first and then a mana pool on top set to receive power, it is possible to dupe mana by dropping a mana tablet into the pool, which is instantly taken out by the hopper without the damage value of the tablet decreasing.
This bug is SOMETIMES 'fixed' when the player relogs, however the mana obtained from the bug remains usable and the mana tablet damage value remains unchanged.
I have not observed this to happen when placing a mana pool first and the hopper under it second.
Updating either block does nothing (updates caused by placing a block)
Droppers directly above the mana pool, facing down into the setup also works.
However droppers directly adjacent to the mana pool, facing sideways appears to not, when it works otherwise.
Using latest everything as at time of this post.
Further testing has shown that the dropper information might not be acurate and the bug might be coordinate affected. :/

The damage value isn't any more than a visual representation of how much mana is in there and not an accurate value, although I'll have to look at this, it might be possible if I forgot a check.

I know that :P, I actually never checked how much mana was stored in the tablet afterwards...
Could you add a debug item for checking the exact amount of mana stored in items? It's hard to tell when durability and the mana pool gui are the only indicators and the mana pool transfer rate is so slow...