Hah, I just went back and tried it, and perhaps I was just too tired at the time, because it all seems to work. Sorry about that.
However, in the meantime I have found RegEx problems, though perhaps its my code?
For instance, the code bellow should return an Array of true and false. However, in Jint it returns true and true. I also tried your test patterns and they seem to be the same, though I might be missing something here.
var hello = "Hello";
var pattern = /Hello/;
var resultTrue = pattern.test(hello);
var pattern = /Test/;
var resultFalse = pattern.test(hello);
return new Array(resultTrue, resultFalse);
Either way I found a way around the above, by exposing .NET functions I needed.