I had spent some time factoring a project's java packages into modules. The problem is intellij does not reliably propagate a module's gradle (maven) dependencies to any _referring_ module.
In other words:
core-module (gradle with maven deps A, B, C)
module1 (depends on core-module) <-- build fails because dep A is not included in class path. if I add class path but then rebuild, intellij forgets class path, or forgets dep on core-module.
Seriously, I will bail back to eclipse if this is a bug.