Add a scoreboard with shears being used as the criteria:
/scoreboard objectives add shear minecraft.used:minecraft.shears
Display it in the sidebar:
/scoreboard objectives setdisplay sidebar shear
This scoreboard objective doesn't increase when mining carpet with shears and the other mentioned blocks.
If you use the criteria "minecraft.used:minecraft.diamond_pickaxe" and use said diamond pickaxe to mine carpet the score for the pickaxe increases, so why wouldn't it with shears?
Another Argument on why this is a bug is that the durability decreases in both cases, so the tools are clearly being used!
I think it might be good to have a list of blocks where it does not work. For the reason that you need to have the block mined with shears to actually collect an item, but where the criteria does not tick up.
tall_grass
large_fern
seagrass
tall_seagrass
nether_sprouts
Confirmed in 20w48a