tclhttpd logs

I wonder if anyone is familiar with tclhttpd log entries and can shed some light on this:
Typically each log entry contains a bunch of attributes including the ip address, a timestamp, the requested url, user agent, http code, etc. But I am seeing an increasing number of weird entries where most of that info is empty. The lines only include the ip address and the timestamp, and the rest is just "- - - - -".
What does this mean?