Hmm. I used to have Roadrunner before switching to DSL, and never noticed it back then. That was over a year ago, though. Either it's some annoying thing that both SBC and Roadrunner are doing, or it's something between your box and CF. Or possibly an OS setting on the box CF runs on. Though, I doubt that's changed recently. Maybe the hosting service CF uses decided to start terminating inactive TCP connections for security purposes?

I'll try it from work with a throwaway lowbie and see if I get the same behavior. If so, then it's probably not anything related to our respective ISPs. Will try to narrow down what the exact inactivity threshold is too.