Went lean...

It sounds like the answer is in the breather setup. Got any pictures of your engine, air cleaner, breather hoses, breather filter etc? Seeing how yours is setup would probably help people visualize if a change to anything might explain your experience.

It sounds like you stopped, fiddled with the air cleaner, and suddenly your idle AFR is dead lean and your WOT afr went from 10 to 13.5 and that neither is a huge concern except you don't yet understand why it happened.

The added info that the behavior or you car changed in the expected way along with the change in the AFR reading is also hugely useful - we know something did actually change with the engines operation. Like Rat alluded to, the AFR can change due to sensor/gauge behavior when in reality nothing in the engine changed. I've experienced exactly this when my O2 sensor on my EFI decided to die over the course of about 20 miles on my way home - 'twas not a fun ride, and the following week of fiddling sucked too.