To answer my own question from the previous post, there is actually a non-trivial example of where the Block Graphics Bug would manifest itself in Manic Miner - if there was a Type 1 Nasty placed in the layout of 'Ore Refinery', then its graphic would indeed be corrupted, because the attribute byte for Nasty 1 (#44) matches a graphical byte from another block type (halfway down the floor tile) that is listed earlier in the cavern definition.
There is also the issue that both of the unused-but-defined nasty graphics in 'Skylab Landing Bay' would not get drawn if a nasty (of either type) was placed in the layout, because their attribute byte is set to zero, matching the first (and indeed all) graphic bytes for the background tiles. However, you wouldn't see the defined nasty graphics in that cavern anyway, even if the Block Graphics Bug was fixed, because 00 = black INK on black PAPER. Therefore I would categorise that as a trivial example of the 'Lurking Block Graphics Bug' (alongside a number of other even more trivial examples, arising from completely undefined cell types whose attribute and graphical bytes are all set to zero).
All of which is to say that, if you were to pass the original Manic Miner through SPECSAISIE's 'Find the Block Graphics Bug' function, you would see quite a few 'BGB Flags' in the output (for various reasons).
EDIT: Andrew Broad's 2008 Remix of Manic Miner has Fire 1 cells placed within the cavern 'Ore Refinery', and they are indeed corrupted by the Block Graphics Bug!
And 'Skylab Landing Bay' in the 2008 Remix contains a black INK on black PAPER Fire cell, which is also blank apart from the bottom pixel-row, which has the following bitmap which flashes momentarily but visibly when Willy is killed:
That is equal to #4C, which is the attribute byte value for the first floor tile definition (which follows on from the background tile definition). So after the topmost pixel-row of the background (non-)graphic matches with the Fire attribute byte, the Fire cell is drawn using the background's remaining seven blank graphic bytes, then the floor tile attribute byte interpreted as a bitmap for the Fire cell's bottom pixel-row (normally not visible except at the point of Willy's demise).
Edited by IRF, 04 December 2018 - 03:56 PM.