This only seems to correctly set the Yoshi coin icon if I've just entered and left the stage in question, otherwise the icon is always empty when moving around on the overworld, even if I have all the Yoshi coins. I'm using SA-1. Any idea why this might be happening?
EDIT: I ended up using the "Yoshi Coin Checker" UberASM instead, which places the same icon but works correctly for me. Not sure why this patch doesn't.