The issues I speak of are indeed the known issues and stuff listed in the patch notes. They try their best to fix what they can with new content before releasing it, but usually there are still a few kinks to work out that aren't too big an issue that should delay the release further. Again usually some bigger issues than expected do crop up but they get hotfixed. By way of example, for Eureka the minor issues consisted of the bit where world names don't appear in party chat and the few other things, and then the big one that appeared they had to hotfix was the elemental level "rewind".