Today I had a weird situation while playing my modern combo elves deck.
Log won't be useful here since it's something about mana pools.
I disactivated the "use mana from pool automatically" checkbox.
I had a
Cavern of Souls naming elf, a
Cloudstone Curio, some more lands and a Fetchland. So I added 1 green mana to play elf spells with my
Cavern of Souls and then cracked my Fetchland, found a forest, cloudstone curio triggered and I bounced my
Cavern of Souls. As I hadn't play a land yet, I played
Cavern of Souls naming Horror because I had a
Spellskite in my hand. I tapped the cavern for Black and another land for green and casted
Spellskite (still should have that green mana only for elves in my pool since it can't be used to cast any other spell).
After that I casted Beck side of a
Beck/Call (still should have that green mana only for elves in my pool since it can't be used to cast any other spell).
Then I tried to cast an elf using the green mana in my pool that I had there the whole time and I couldn't use it... Not even activating the "use mana from pool automatically" checkbox again.
So what I think is happening (I might be wrong) is that cavern of souls is missimplemented so that the mana you add with it can be used only on the creature type that is currently chosen, and not the one that was chosen when you activated it for mana. I couldn't confirm it since I didn't have enough mana to play an elf with another land and then bounce
Spellskite with
Cloudstone Curio to recast it using that exact mana.
I hope I explained clearly since I'm Spanish and my english is not perfect.
FIXED