Guide Shape Changes After Duplicating a Part of Base Mesh 

 

Problem 

When you have set up your hair stack with topology-dependent operators like Edit Guides operator and Surface Comb operator selecting some faces of your distribution mesh and using Maya's Duplicate option corrupts the strands in the stack. The shape of the strands changes and/or jumps to a different position.

 

Cause 

Sometimes mesh objects in Maya can have strange triangulation and topology. This is especially true if importing the mesh via FBX or Alembic. When duplicating some faces on this mesh the triangulation can be changed by Maya. Because some Ornatrix operators rely on the mesh's topology to remain constant the results of these operators will also change.

In many ways, this is the same issue as strands flipping on a deforming base mesh.

 

Solution 

As in strands flipping on a deforming base mesh, go to the base mesh attributes and change the Quad Split option to Left or Right to restore your strands.