Using shorthand *= leads to unexpected result?

[Michael via Digitalmars-d-learn]

It may be that I'm doing something wrong here, but after updating 
DMD to the latest version, my simulations started producing some 
very odd results and I think I've pinpointed it to a sign 
inversion that I was making. Here is some code from dpaste to 
demonstrate the behaviour I get vs. the behaviour I expected:
https://dpaste.dzfl.pl/9bd7aea75fb2

Any ideas? Am I getting something wrong or is this some sort of 
regression with the latest DMD?