URL handling of archive plus cat parameter changed in 2.3

I found that turning of the canonical URL rewriting restores the previous behaviour. But that may have other unwanted side effects.

Another option is to hack canonical.php to let category URL’s pass without change. But I don’t like changing a core WordPress file.

Any ‘less hacky’ way of doing this? I thought combining parameters like this wasn’t possible until i stumbled across someone who managed it, and now it turns out i need to downgrade three versions to make it work. Sillyness.