broken exit node
Some exit node is stealing failed DNS requests and redirecting to guide.opendns.com. I don't know which one or how to find out, I suggest doing a full scan.
[I know this is probably the wrong place to report this. I won't report this outside of Tor to prevent corrolation attacks between my use of that exit node and my reporting the problem. There should be a way to report potentially sensitive Tor network problems anonymously from within Tor without needing an email address. I suggest a tracker component "Tor-Tor network".]