We have had a problem for a while now with some new Javascript we did using jQuery where SOME people using IE7 and IE8 would be reporting as IE6 and thusly causing a lot of the code to break. After lots of head banging I found out the user agent was this:

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.0; Trident/4.0; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) ; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 1.1.4322; .NET CLR 3.5.30729; .NET CLR 3.0.30618)

Or with similar mutilations.

I have however found a work-around that seems to be working with no ill effects.

Line 1170 of jQuery:

version: (userAgent.match( /.+(?:rv|it|ra|ie)[\\/: ]([\\d.]+)/ ) || [0,'0'])[1],

with an added question mark in the regex here at the beginning:

version: (userAgent.match( /.+?(?:rv|it|ra|ie)[\\/: ]([\\d.]+)/ ) || [0,'0'])[1],

It might be worth applying if you see it working well, seems to be good on ours.