After some time of research I found the following:
If I use table components in my reports the will never render any data, unless they can successfully locate a 'Dataadapter'.
This is especially annoying when I want to pass explicitly the filled JRDataSource for filling the report.
Removing dataadapter references from the jrxml doesn't help as well.
Only workaround I see currently: Implement a custom Dataadapter using a thread local to pass the previously created datasource.