Just for reference, if you come across one of the following problems:
Validation only datasource
Looking at the options of dbCreate in Datasource.groovy I only found 3 values: create-drop, create or update. But there is a fourth one: validate!
This one helps a lot when you use schema generation with Autobase or doing your schema updates external.
Controller.redirect has two options for passing an id to the action id and params, but if you specify both which one will be used?
Trying this out I found the id supersedes the params.id.
Thanks to Burt and Alvaro for their hints. I submitted a JIRA issue