Win10 SDK is UDP protocol example. UDP protocol itself has some limitiations.
URR is (experimental) protocol based on UDP that adds some bookkeeping data to UDP in an attempt to "fix" these limitation. That is why there are data missing when you recieve UDP datagram - URR interprets the beginning as header.
Frankly, it is low importance project, that is why it is not in "canonical" U++ (uppsrc). I have uploaded it into bazaar because I have it developed for some project that was later abandoned, it works, it is tested, but has limited utility, unless you hit the same usage scenario (single server that has to process thousands of requests per second - HTTP is too slow for that).
If you desperately need UDP in U++, well, it is really trivial and you can cut those lines of code from URR.