Assuming I'm understanding the issue correctly where flawless means it doesn't play cleanly without buffering or skipping things.
It's most likely related to the bevy of advert handling changes that were introduced in 2.5 (I cannot comment much on this final 2.5.1 release but it's likely a lot of what I'd done as part of what was to become 2.5 is still in there albeit not finished off) to try to control the stream output so that adverts would be correctly inserted & the stream would resume back in at the correct position.
Setting
ratelimit=0 in the DNAS's config file is the first obvious thing to try which if not using the DNAS+ / advert stuff is the best thing to do anyway (which makes it act more like the 2.4.7 release). As despite RN locking access to the downloads down, etc there's a lot off good things in 2.5 to make it work better with HTML5, make it easier to connect sources and other related usage.
Sadly they're not properly updating the changelogs at
http://yp.shoutcast.com/v/ since I was let go to know what has actually been done other than a single generic one line at the very bottom.
So if that
ratelimit option doesn't work then other than trying to report the issue to SHOUTcast, going back to 2.4.7 is probably the best option. As for the YP listing stuff, it's all a mess with them locking things down to need an account (which doesn't really work in hosted setups i.e. the majority case) but afaik the older 2.4x way of doing things should still work (has been a while since I've tried myself. Alas the authhash system never really worked as wanted (a known point of data to resolve listing related issues) as it went against the connect & go approach people wanted (though registering on other directories was deemed ok, heh).
-dro
Problems with Shoutcast 2 "mp3"