I tried to change the chunk to any darklands specific biome and the biome changed to ocean when holding only one creeping moss. This seems to be fine when holding 2 or more creeping moss - it changed ok.

Thanks for the report, I will look into it.

It looks like this issue was simply a description error, where the item was destroyed before the usage message was sent, thus the default biome of ocean being displayed. The biome itself would be updated correctly however.