Wilbur Jagged Coastlines

[Eusebio Ptolomeu]

I'm having a problem with Wilbur, recently. I like to generate heightmaps in Blender and send them to wilbur so it can calculate erosion. I mostly use Wilbur precipitation-based filter for this (lots and lots of passes, too). Normally I'm able to achieve good results with it, but sometimes I notice that the final image gets a little too noisy. This is only a major problem when it comes to coastlines: I end up with a "jagged" coastline with lots of intermiten sea and land pixels. Take a look at this picture, for example:
world.png
Notice how the coastlines seems too jagged in some places. I tried changinging lots of settings, both in Blender and Wilbur, to try to solve this (blurring the heightmap first, a little/ messing with the parameters in the Precipitation-Based filter) but I always end up with this result for most of the maps. For some of them, however, I don't seem to get this kind of jagged coastline. I'm trying to understand what makes such heightmaps give good results, while others don't. As I said, I checked every little parameter I could in the workflow of both kinds of map, and both of them are exactly the same (same way to generate the map in Blender, same parameters applied in wilbur, etc.). Does anybody knows what causes this kind of result? Is there a way to adress this?