I get tons of those as well. All coming from IE9 and exactly 14 seconds after another request. I couldn't replicate it with my own IE9 though :-/

It's a bit random if it occur after a script or not, except for one ping-script I have, which doesn't use KeepAlive (header "Connection: Close").

This ping-script is called from a Flash file, so it can't be google-mouseover-previews.

The error-log is filled with: "Request header read timeout"

I'm planning upgrade Apache to 2.4 an see if it changes anything.

I'll keep you posted.