While experimenting with custom worlds, I found that when setting a terrain with empty areas at depths of y = -54 and below, lava is generated there instead of water, regardless of the default_fluid set in noise_settings. It happens in any dimension. Probably, it’s the reason of some bugs with generating of lava in custom carvers. Setting sea level lower this value doesn’t help, in any case lava is generated on this level.

In order to see the bug, it’s enough to create a world with “factor”=0, to delete the bottom_slide and to set default_fluid as water for clearly visible effect. The bug also appears with other settings.

It’s expected for this settings that water will be generated from bottom to sea level at least outside the carvers.

In fact, water is generated above y=-54, lava appears below.