This is a wonderful method and implementation that I have used frequently, and always successfully. If I had one "feature request" it would be the option to restart a prior optimization by reading the optimResult file and starting with the current population in that file. I have, on occasion, had a problem terminate prematurely for reasons having nothing to do with differentialevoluion.m. It would be nice to continue such problems where I had left off.
I think I found a crucial bug: in my program I write down the test parameters if they fit better than in the iterations before. In my test PSO stopped after fulfilling a break condition and gave me a final parameter set, which fitted less than an intermediate result I wrote down before.