Bottom solid layers setting apparently not honoured (v2.5.59) is this a bug?

[NameOfTheDragon]

Hi. I've been testing v2.5.59 with the Arachne engine, and mostly I'm getting great results. I noticed something curious and I'm not sure whether it is a settings issue or a potential bug, can you please comment?

See the screen shot below. I have bottom layers set to 5 and "minimum bottom shell thickness" set to 1.2 mm and I'm using 0.2mm layer height (0.3mm first layer). So 5 solid layers ought to take me up to 1.1 mm. I've noticed that on some parts of the model, I am getting sparse infill instead of solid infill much lower down. In the screen shot, you can see sparse gyroid infill on layer 3, which is at 0.7mm. Why don't I get the full 5 layers or 1.2 mm of solid infill?