MMU2S Mesh ordering breaks when two meshes use the same extruder

[JasXSL]

Version 2.1.0
Windows 10
MMU2S

Using MMU2S you can change the priority of overlapping meshes by changing their order in the list on the right:

The problem is that when two meshes use the same extruder, said priority goes right out the window. In this one I wanted the blue (calico_base.STL) to also be white. And this happens:

Here's the file:
calico.zip

I suspect it's ordering by extruder rather than model, which would explain why it turns completely white. It would be nice if it could order by model instead of extruder.

[bubnikv]

In PrusaSlicer 2.4.0-alpha1 the order of the object volumes in the right panel will be respected, the object lower in the list will win.