Negative response time?

We just moved our quixote application to a dual-core (AMD athlon x2)  
server. I checked quixote's access log, and saw negative response  
time at the end of the lines:

59.48.38.120 - 2006-02-12 17:50:19 17810 "GET /movie/ HTTP/1.1" 200  
'Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; (R1 1.3))'  
-1.77sec

not that it matters, and it's probably not a quixote issue per se...  
but what went wrong?

it is running on gentoo linux (2.6 kernel). Incidentally mysql-super- 
smack sometimes shows negative connection time as well.

- Bo