An extension is not an extension point

I'm currently working for a customer in an RCP project. There is a lot of work to be done and we are around a dozen of programmers actively contributing. A couple of weeks ago we had a strange problem.
One of the core plugins of the app defines an extension point which is actively used by other components. At some point these extensions were not loaded anymore. After quite some time of guessing we found that there was a new plugin using the extension point. But instead of defining an extension the developer (not really familiar with the Eclipse extension mechanism) had defined an extension point. He named it exactly as the existing one and used the original schema file by referencing it from the original core plugin. I was somewhat surprised that the framework did not complain about this duplication, but the main lesson to learn is certainly that there is some basic RCP mechanisms every developer should be familiar with before contributing.