Ladders stay at mid air without support blocks

I was in a superflat world and I wanted to do a giant 3 by 3 waterslide, so I went to the height build limit and did "/fill (coordinates) (coordinates)" then I pressed "tab" and then"enter" but unfortunately it put me ladders and not lapis and so it lagged very much because all the stairs destroyed exept for 1 column which stayed. Now I have 60 fps but even if I try to destroy some of the bottom ladders, the rest of them remain without any support block. I'm not sure if it's a real bug or just a known thing, but I reported it hoping it would improve the game.