Thanks WackyToaster and Karentzos, I appreciate the support.
I'm going include a simple function so that convex polygons with up to 8 vertices will definitely not get broken down, so you can design shapes that won't get decomposed and elicit this bug.
I'm comparing two separator algorithms at the moment. One based on Earcut triangle decomposition and the other based on Poly-Decomp by Schteppe, both from GitHub. The each have their strengths.
Then I've got some more examples to make, to demonstrate how to use the plugin. And then I'm running out of excuses to not release it...!