Thanks, I opened up the bug
https://issues.jboss.org/browse/AS7-5255
Even with logging.properties there seems to be an issue and I'm wondering if this might be related
Configuring the root logger works fine, but it does not work to configure categories
https://community.jboss.org/thread/203159
Interesting is also that I tried even to debug into the loading of the configuration (breakpoint in PropertyConfigurator) and this sometimes resulted in the thing actually working, I'm wondering if there could be some timing issue with this file (or the general deployment specifc log configurations) beeing loaded.