Ask HN: GMail reads and archives mail on its own

Yesterday evening I had 25 letters in my inbox, 20 of which were unread. When I woke up this morning, I found only 5 unread letters in my inbox, all of which were received during the night. Those 25 letters that were in my inbox in the evening were marked read and archived.

I changed the password and went back to bed wondering what's going on. When I came back in about 2 hours, my inbox was empty and all the unread mail received this night was read and archived.

I'm sure nobody knew my passwords, especially the new one I set this morning. There are no filters set up; I checked it. I'm running Safari on Mac, if that matters.

My bet is that it's a GMail bug. What's your opinion? Did anybody else experience the same?