That SHOULD be somewhere in the patch notes, might have forgotten it. It's intentional - I'm trying stuff to balance channels - that one doesn't seem super popular (and hard to explain) so it will likely change somewhere in the future.
Great to hear you're enjoying the game though, and thank you for the support! Sorry for the confusion on that one - this game is very much a work in progress as I try to nail down what makes a good game.
Getting channels 'right' has been a challenge, they're very strong (which is okay) but I wanted there to be some kind of tradeoff for having a ton of them - might try channels reducing max mana instead of upkeep? Gotta think about it.