Eclipse content assist with maven project not picking up all classes

Question

I'm using Eclipse 3.5.0, and have imported a maven project using the import maven project from SCM wizard (M2 plugin).

I have a jar file as a dependency in my pom. and inside the jar is a complicated schema - with quite a number of XSD's. But the content assist doesn't seem to pick up the schema at all, nor a number of other classes in the dependency list. yet for another module in the same project it seems to work ok. Does anyone know why this is? it's driving me mad!