Are you positive? I'm pretty sure it shouldn't. They're definately not equivilent on my server.
I know you should use '&' when outputting an amersand in content to conform to web standards, but i've never seen it used in the url, and i'm 99% sure it doesn't work nor does it belong.
The bug can be seen again when you first change the manufacturer in the drop down and then try sort those results by, say price. You end up with a url string that looks like:
xxx.html?sort=5a&page=1&sort=4d&filter_id=43
It's a minor bug in an otherwise great contribution.