During all the years that I've been using Maven I haven't run into any issues that were caused by a bug in the Maven core. Issues which I know of, I should add. I might just have been lucky or possibly I have run into a bug but blamed it on some plugin. However, during the last couple of weeks I've been running into two bugs in the Maven 2 core. They were both a kind of an edge case, but when built with Maven 3.0-alpha everything worked!
The first issue was from the mailing list, where building a multi-module project involving a SAR archive did not work when building just to the package phase. I am guessing here somewhat, but I think the problem lay in the reactor in combination with a build extension packaging (for the SAR archive).
The second case was something I ran into when building a two-level multi-module project including a Java EE 5 EAR archive, which had a lib directory specified. Also, a workaround with a 'client' type classifier was used to get a ejb-client jar to be placed in the lib directory (MEAR-85). When building from the EAR project or one level above, it worked just fine and the ejb-client JAR was placed in the lib directory. But when built from the top level, the lib directory specified was ignored and the ejb-client JAR was placed in the root of the EAR.
Both issues existed with Maven 2.2.1, but not with Maven 3.0-alpha-3 and 3.0-alpha-4 respectively. And now 3.0-alpha-5 is out, with an even more improved formula. Don't let the alpha name fool you, to my experience it is the best Maven ever. If you run into some issue with Maven 2.x, be sure to try out the latest Maven 3.0-alpha - I wouldn't be surprised if it solves your problem!
