I've had the same issue. Kinda messed up my testing world.. as @LaserSlimeHD said, we should have a 20w12b snapshot to fix this issue. But I can wait till next snapshot 🙂
This is now a bug in 19w13a since skeletons don't spawn above water or in the air and only spawn on a block that is nearby. This is annoying for my skeleton farm. :/
Oops sorry about the duplicate I searched up the words "Player Head" and the duplicate did not show. Sorry. 😞
Isn't it supposed to be like that? "Edit Sign Message" looks rather weird.