What IE configuration contains "MSIE 8" and "MSIE 6"?

Question

Anyone knows what kind of configuration leads to MSIE 8 report a string which also contains MSIE 6 (stripped down version to minimums)?

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)

It's no problem to workaround (sniffing education is not necessary, I'm aware of the evilness), but I'm interested in getting some background what's possibly causing this.

I've seen on this on a co-workers home machine too and we couldn't figure out what would cause this.

Update:

Just today I've had another example of such a "weird" configuration; some customer reporting a problem with embedded video and I immediately noticed this "nested" User-Agent:

Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.1; Trident/4.0; Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1) ; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729; .NET CLR 1.0.3705; .NET4.0C; .NET CLR 2.0.50727

Answer 1

Is it possible that IE8 is in compatibility mode? Are there plugins installed?