This is, at least seemingly, because non-US dialects of English weren't updated in 26.2 Snapshot 3, as also seen with MC-307527 (relates to the Sulfur Spike). With it being changed in English (US) from Polished Sulfur Block it seems as if it wasn’t updated for other dialects.
Confirmed this through my own testing last night
Additional details I’ve found through testing
The ghost blocks still have collisions
Placing a block where there is supposed to be sulfur, potent sulfur, or a magma block makes that block appear
Can reproduce in 1.21.11 and I can also attest that is always happens when using a hopper Minecart beneath the jukebox.
It can be stopped by reloading textures (default is F3 + T) but that reallly shouldn’t be necessary
Seems to occur because the disc is starting and stopping on the same tick