In jquery-1.2.6.js, it tries to extract the browser version from navigator.userAgent
version = (navigator.userAgent.toLowerCase().match( /.+(?:rv|it|ra|ie)[\\/: ]([\\d.]+)/ ) || );
My version of IE, gives following value for userAgent:
Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; GTB6; User-agent: Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; http://bsalsa.com); .NET CLR 1.1.4322; .NET CLR 2.0.50727
As it says, its IE 7, but the eager fetching by the regex used, generates the value as 6.
As clearly mentioned in 1.3 release notes, jquery doesn't use browser detection anymore. But since my guess is, most of users might have not yet upgraded to it, so thought of reporting it.