Not at my development computer at the moment, but I would venture the client has "automatic redirects" enabled in Ultimate URLs... And someone (or bot) is sending unusual request URIs to the server (with malformed data)...

Out of curiousity can you verify my guess by examing the corresponding request URIs from the webserver "access.log" around the time of those warnings?


Would not worry too much, but you may want to upgrade PHP as the warning is only generated under PHP 5.3.2 and older (past EOL).