Sea level world generation bugs

This bug is similar to MC-61947, but it's slightly different so I thought it better to create a separate report. Lowering the sea level causes abandoned mineshafts to generate aboveground. I assume the reason for this is that normally the mineshaft sees water there and so doesn't generate, but with the water gone, it sees that the location is below level 64 and so thinks it is underground. This bug might also happen with strongholds but I was unable to confirm that.