WilliamWIkked's question isn't that wrong. Even stable softwares may have bugs. If you know of one, you might want a fix, that's the reason why you would ever want a new release of a stable software. And there's no perfect program, you know. (So I suppose HERZ just hasn't seen any problems yet.) However, you, as a user of UnrealIRCd, can do a lot to make it as stable as possible by reporting a bug to the developers whenever you find one.
In case you can't wait for a new release, try out the current development code from
CVS, it may contain some fixes, however, at the same time it can be unstable as well, so probably you don't want it on a production network. (More info in the
FAQ.)