I've reported many strange bugs to jcupitt and I can speak to his really helpful and patient nature.

My favorite one was when JPEG2000s that had an even width was being shown in greyscale on any mac app: Preview, Safari, Pixelmator, etc: https://github.com/libvips/ruby-vips/issues/345

All images with an odd width was working fine.

However the real bug was to do with chroma subsampling (and a lot of other technical stuff that I don't really understand): https://github.com/libvips/libvips/issues/2965