Edit Poly vertex displacement

[UmarAR]

When adding an Edit Poly Modifier to my Editable Poly Stack I sometimes get an unexpected geometry changes with some of the polygons created from the individual spline shapes on my Edit Spline Modifier below. Some of the verticies jump to other vertex points with extra vertices being created in the process.

Also when I move between the Edit Poly and Edit Spline Modifiers upon switching back to the Edit Poly Modifier sometimes all the polygons are of the correct shape.

However the issue persists.

Currently my solution is to copy the polymodel when of the correct shape and collapse the stack. Then proceed to work further on it.

Thanks.

[CAMedeck · Accepted solution]

If you add an Edit Poly (Mesh, Spline, etc.) modifier on your stack, I highly recommend not making edits below it.  That Edit X modifier assigns a number to every vertex, segment, spline, face, etc. and uses that number to remember what is getting edited and how.  If you change something below and that adds or subtracts one of those elements, that will change the numbers assigned by the Edit X modifier which will cause problems.  

A simple way to see this in action is to draw a Circle and add two Edit Spline modifiers.  In the top one, move the right vertex to the left, making sort of a crescent shape.  Now in the bottom modifier, click Refine and add a new vertex just above the rightmost vertex.  When you go back to the top Edit Spline, you'll likely see a much different result than before.