I have a similar problem, but on a different frame:
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I still can't believe I hadn't noticed this bug until now, seeing how 1.4.2 was when I started playing, and that millions of others haven't noticed or have shrugged it off.
Still in 1.8.3! Come on Mojang!
Actually, I remember them mixing in Official Release 1.5.2.
I encountered this problem on a vanilla server in 1.18/1.19 after building an 8-beacon array at the bottom of the world underneath a 5-story house at sea level with a conical roof on top, and all the blocks above the beacons are stairs or slabs or pressure plates or doors. I am not going through the effort of demolishing even a single column of that just so that I can get the advancements, thank you very much! >:[