This is a bug that Milan fixed in H2D and we still have it in H3D:
Corrected a bug where the meshes of u_ext's were not taken into
account when constructing multimesh assembling stages.
This is still present in H3D and should be corrected - it e.g.
caused segfaults in neutronics-heat-conduction-adapt.
This is a bug that Milan fixed in H2D and we still have it in H3D: