This is a bug in GWT 2.5.1: https://code.google.com/p/google-web-toolkit/issues/detail?id=8369
It reports that type as public although it's protected. Our logic correctly checks for isPublic:
Until this is resolved, it's prob. best to up/downgrade your GWT version. If that doesn't work, we can consider building in a workaround and use reflection to check for the modifiers for nested classes/interfaces.
GWT Bug is not fixed yet - switch to 2.6.0 doesn't help.