EM-5 focusing desaturation effect
Playing around with a OM28mm I noticed that when I focused on a broom (the witch kind of broom not a push broom) that the bristles took on a desaturated effect when they were in focus, or close to focus. Noticed the same effect with my m48mm under auto focus. It was very pronounced when the broom was in good light.
Something to do with the pattern frequency me thinks. Sort of a built in focus peaking for brooms. Go photograph the bristles of your broom from 10 or so feet in good light if you have nothing else to do.