That's probably because the news.ycombinator.com certificate is rooted an Entrust certificate thumbprinted "50 30 06 ...", trusted by Windows [1] but not Windows Phone [2].
Yet another reason Apple's "one and only one way to do it" approach to code signing certificates may not be such a bad idea after all.
Interesting. I had some initial problems with installing the certificate for blurity.com when I got the intermediate cert chaining backwards, but this is the first I've heard about problems since I fixed that a few months ago.
Could you drop me an email at the address in my profile? Thanks!
A quick Google search turned up this [1], this [2], and this [3], all which seem to indicate that StartCom certificates were unsupported on Windows Phone, at least as of 7.0 RTM. So the problem may indeed be as simple (and frustrating!) as an untrusted root.
Yet another reason Apple's "one and only one way to do it" approach to code signing certificates may not be such a bad idea after all.
[1] http://social.technet.microsoft.com/wiki/contents/articles/2...
[2] http://msdn.microsoft.com/en-us/library/gg521150(v=VS.92).as...