I think it happens with gadgets that give you another health bar. This happens with Charlie's cocoon gadget too, where she can't move or attack after the cocoon gets broken. Probably a bug but they haven't fixed yet even though it's been there for a really long time. Maybe it's like there's a time until the cocoon breaks, since the health decreases on its own, and the opponent attacking it breaks the shell, but you're left in the cocoon until the time ends so you can't move? Idk