Background: You're a browser. You want to follow all the standards. But you also want to provide a way for people to override things for your browser, in case you do something wrong.
Recommendation: You should obey the special <renderername>hack (e.g. khtmlhack) media type. HTML authors can use this in such constructs as:
@import url("stupidk.css") khtmlhack;
@media khtmlhack {
/* style sheet for khtml goes here */
}
<link rel="stylesheet" type="text/css" media="khtmlhack" href="stupidk.css" />
This is safe, since it introduces no new syntax and all developers are warned (in bright green): "Note. Future versions of CSS may extend this list [of media types]." Simultaneously, is unlikely that a future CSS specification or anyone else will define a media type khtmlhack.
Conclusion: This should be adopted since it is easy for authors to use, it won't choke other browsers, and it won't conflict with anything else.