Bug: "Ghost blocks" - Can disable blocks by flinging onto them when they are at top of stairs

[wisprabbit]

Reported by Muftwin in relation to Slightly Low Basement. Spelling ERA in this spot, and then getting on top of the A, breaks the word:

After tinkering with this, I think it is a bug to do with flinging up stairs onto blocks, and you don't need the ERA spelling to trigger it. Steps to reproduce in Slightly Low Basement:

1. Destroy the A or R to rebirth a block on the upper floor.
2. Push the rebirthed block south, then east, to place it at the top of the stairs.
3. Drop down to the lower floor. Walk up the stairs until they bend to the north.
4. Fling north. Emm should land on top of the block.

On the next turn, the block becomes what Muftwin calls a "ghost block". When you walk into it, instead of breaking it, Emm will step on top of it. The block is no longer recognised as a letter for spelling words.

I recorded this video which reproduces the glitch:
https://www.youtube.com/watch?v=9sMFUbb6QEs

I recorded it while trying to reproduce Muftwin's screenshot, so there are some unnecessary steps in there, but the video also demonstrates:

• Flinging on top of the block is an important step. Walking up the stairs breaks the block against the wall as expected.
• The block becomes a ghost block on the turn after the fling. ERA is recognised as a word on the same turn as the fling, but then becomes transparent when I step away.

Muftwin adds: "If i had to guess what happened id say this. i am walking up the stairs therefore i should go above the a. then check if im pushing the block it checks the square where it actually is, but when the breaking code triggers it breaks the spot i am moving to. now it has become a ghost block similar to the groldy bug i posted. ghost blocks are a bug of course so it makes sense that i cannot spell anything with them."

The "groldy bug" is issue #22, which has a similar result (a block becomes non-interactive) and is probably related.