I don't find there's any problem with it refreshing while i type a quick reply, regardless of the time i spend (at work sometimes i get interupted and come back 1/2 an hour later). So it's probably something with your browser. My best guess is that it's some sort of spyware or adware causing your system to do this. You might want to go to www.lavasoft.de
to get the program "ad-aware" it looks for programs that attach themselves to your browser and cause random popups and report back your surfing habits. Many of these spyware programs piggy back themselves on "free" programs such as download accelerator, the weather bug, any sharing program such as kazaa, grokster, etc.
If it's "free" it usually costs you in bandwidth and now that many isp's make you pay for your bandwidth it costs you in money too.