Bugs and feature requests for RAP are tracked in the the Eclipse Bugzilla.
Reporting a bug takes only a few minutes. Start here:
Choose a short and concise title and include the following information in the description:
If the reported problem is not obvious, a simple snippet may be helpful for us to reproduce the issue. If you report some visual misbehavior, a screenshot helps us understand your problem. Remember that we don't have your exact desktop environment and browser.
Even if issues appear related, every problem deserves its own bug.
If you're not sure if a certain behavior in RAP is really a bug, you can ask on the RAP forum before. If the issue is related to RAP's implementation of Eclipse APIs like SWT or JFace, you should try your snippet in SWT and see as it works as expected there.