It's just the way Google handles typos/synonyms and the way it tries to understand the context.
Does shifting the words change the phrase's meaning? Actually, the best way to answer this question is to look at the 6 sites that rank above you for the "green best widget." Are they your usual competitors or are they entirely different sites? What is the content like? And how is it different from what Google serves for "best green widget?"
But most importantly, have you confirmed that "green best widget" and "best and green widget" get any meaningful monthly search volume? I've noticed that in most cases it's better to concentrate on long-tails (like "best green widget for sale" or "how to use the best green widget") rather than chase after the typos.