Which subtlety? Your object [substitute part  ] has 2 spaces at the end. So the second space is used as replace value instead of default 0.

well i think it was subtle :x plus i wasn't able to actually create a [substitute part ] with 2 spaces at the end. Whenever i type it in an object box it is reduced to no space at all. Had to copy past it from the omx.comp helpfile. it's nothing much really

i mean, visually looking at this helpfile and trying to recreate the same behaviour, took me a while to understand why i had a 0 instead of a blank space