This just happened again, so I thought I’d mention it:
When I’m reading here, I go to a forum, browse down the page, click into a thread I want to read, then, if I don’t post, click the back arrow to go back to the forum page.
What has happened at least a half dozen times over the last week or so is that instead of going to the previous page, I go to the page before that, which might be elsewhere in the SDMB site or might be wherever I was elsewhere on the net prior to coming into the Dope. (My bookmark takes me to the MPSIMS forum page, so if it happens in the first thread I read in MPSIMS, two clicks back would be offsite.)
If I check the dropdown, there’s no sign of my having been on the intervening forum page.