context.xml is not copied into war anymore

When I add this line to the config:

<containerConfigXML>${basedir}/webapp/META-INF/context.xml</containerConfigXML>

I can see that the plugin takes the parameter into account:

[DEBUG]   (s) containerConfigXML = D:\workspace\GktGwt\webapp\META-INF\context.xml

but the resulting war file doesn't contain a context.xml file in META-INF/. I also don't see "adding entry " in the debug output so my guess is that something removes this entry.

I also cannot add this entry via dependentWarIncludes or webResources which suggests that there is an invisible filter which just trows all these items away.