With a constant spring resting length, diagonal springs can introduce wrinkles.

The new one-spring-per-edge system can explode too(left). The new pseudo-spring-system can't (right).

Here you see static meshes that are simply submited to the API every frame outlined in green, meshes which have spring forces applied to their verts outlined in yellow, and meshes which are being generated every frame outlined in red. These colours reflect the relative expense, so green is good and red is bad while yellow is in the middle. In this sequence an edit operation in the foreground sets verts there into motion, causing forces to be propagated to the verts of the meshes in the middle distance and then onwards untill the wave of motion has reached every connected mesh. I turned up the simulation timestep for the final image to produce a computational explosion (TOTD: hit the "Snap Verts to Grid" button if that happens when you don't want it to).