KODE's Mercurial repository is hosted on Bitbucket, at:
A mailing list for developers and users is hosted on Google Groups:
Bugs can be reported in the Issues Tracker page. Even if you report the problem in the mailing list, it's a good idea to submit a bug report so it won't be forgotten.
The easiest way to submit patches is using Bitbucket's ability to fork the repository, commit (and test!) your changes on your own repository, then create a pull request to merge it back into the main repository.
Note: whenever you submit a non-trivial patch to fix a bug, it's a good idea to create a minimalistic test case in the test suite that demonstrates the bug that was just fixed.