Zyra seedling bug

I haven't been able to test this fully yet, however I believe that Zyra's seedlings, even though they state that they only use seeds or one charge of the seedlings, are using mana. I'll be low on mana (have about only enough mana to cast one spell) and then I'll use a seed so i can proc it with a q or e. After I place that seed, I'm suddenly oom. Tried with a full mana bar, just placing the seed, but the mana bar didn't go down. I've had that happen many many times (tried with normal skin, and haunted zyra skin). I've been meaning to test it more fully, but really haven't had time. Hope someone else has had this happen to them....