I managed to miss this news story a few days ago, It also seems it has not been mentioned on IIS.
I thought it was interesting anyway.
8th April:
'Mystery' Light on Mars Spotted by Curiosity
9th April:
NASA: 'Mystery' Mars Light not so Mysterious
Apologies if this is posted elsewhere, I did check but couldn't find anything.
Not sure I like the cosmic ray theory, as the spot appears on the ridge of a hill in more than one photo. Plus it just doesn't look right in the zoomed-in view.
I think tho the reflective rock theory has some validity.