I just tested this in 1.18prerelease5. There are now only occasional holes where the old alpha-generated terrain had gravel instead of stone in a bedrock "hole". The gravel fell out into the void and left behind a proper 1x1 or 1x2 air hole in the bedrock. This hole is then converted to a hollow 1x1 or 1x2 shaft by prerelease5.
Maybe the algorithm could check that the bedrock hole is bigger than 1x2, and only then generate a hollow shaft? Maybe a minimum size of 2x2?
af12689
I just tested this in 1.18prerelease5. There are now only occasional holes where the old alpha-generated terrain had gravel instead of stone in a bedrock "hole". The gravel fell out into the void and left behind a proper 1x1 or 1x2 air hole in the bedrock. This hole is then converted to a hollow 1x1 or 1x2 shaft by prerelease5.
Maybe the algorithm could check that the bedrock hole is bigger than 1x2, and only then generate a hollow shaft? Maybe a minimum size of 2x2?