When running tests from multiple instances of NUnit, occasionally I experience a bug where command requests are routed to the wrong remote control if one browser closes while another is operating. The hub and all associated remote controls (two *iexplore, two *firefox) are running on the same workstation as NUnit. This issue concerns the Internet Explorer 7 remotes, but I've seen a similar effect on Firefox. In particular, a new session ID (call it 30900) was opened on one remote control (call it "Remote 1") via ISelenium.Start(). Shortly thereafter, the open session on Remote 2 was closed via Stop() from the other instance of NUnit. Then the first instance of NUnit issued an Open(...) command intended for session 30900, but the hub routed this request to Remote 2, instead of Remote 1 where session 30900 was opened.