noticed it as well.
one of the last patches they changed how big rocks interact with the environtment: for instance, before as a ghost you would get right through them, while now they have an interaction.
in the process however, I think the "mining window" (ie the spot on the rock where you get the message that you can mine it it R) changed as well. I am not sure, but I think the rock itself and the mining 3d area i nthe engine are 2 separate entitites. now that the big rocks got changed, somethign happened to the mining window as well
indeed, for some rocks you can still find one small mining window if you manage to get very close to the center of it, whereas before the same rock held 2-3 independent nodes.