Rechecked this now, and it's at about 5% now. The statistics seem a bit weird to me, unless there are some big seasonal changes. Your 12% was recorded in June and July. Maybe with less business activity during these months, the Windows share plummets in favor of home users who are more prone to use Linux.
Percentage is not as easy or helpful to work with, when there are orders of magnitude difference between absolute numbers. It hides the absolute number difference for no other reason than unspoken lying of statistics.