EAP 139.1.20: Encoding problem with Java compiler

When compiling Java sources that contain special characters like German umlauts, the class files generated by the IDE compiler turn out different than when doing an external compilation; this breaks some of my unit tests!

I am using the latest EAP build but can't say when this behavior was introduced; it does not occur with IDEA 12, though.

Am I missing some configuration setting, or is this in fact a bug?