Konqueror, other browsers: "unknown host", WTF?!

Question

Every once in a while, Konqueror gives me the following error page after trying to load a website:
An error occured while loading [page of website]:
Unknown host [website].
Trying again will *always* result in the page loading properly - this stuff happens when my internet connection is solid.
Dillo gives me exactly the same problem. Interestingly, Firefox and Links/eLinks don't. It seems almost as though the problem's rate of occurrence is related to the rendering speed of the browser, though I doubt that's the case.
More interestingly, Firefox and Internet Explorer are both affected this way on another computer in my house. Other machines are asymptomatic.
This problem appeared following the installation of a new router, a Dynex DX-E401, after the old one was fried by a power surge.
Changing the MTU used by the router has not helped.
What is going on?

Answer 1

I'm not qualified to say anything good, bad or indifferent about anything related to kde, but in general, disabling IPv6 unless you actually need it is a good thing, IME. I always exclude it from my hand-rolled kernels - that way I don't need to worry about any related config in userspace.
By comparison, I've recently put OpenBSD onto a freed-up partition on this machine, and as I don't know enough about it yet, I'm using their stock kernel. The logs have frequent entries about IPv6 connection attempts failing - not surprising, since my lan knows nothing about it.