The current tree has dev-java/jibx versions 1.1.5-r3 and 1.2.6-r1 .
However, <dev-java/jibx-1.30 does not work with JDK 1.8 . See developer comment at https://stackoverflow.com/a/40468425/1132250 .
As early as 2016-11 there have been updated releases 1.3.0 and 1.3.1 (see https://www.sourceforge.net/projects/jibx/files/jibx/ ), but they are currently not available in the Portage tree. According to this report https://github.com/jibx/jibx/issues/5#issuecomment-266452729 , jibx 1.3.1 fixes the issues.
Affected packages are for example app-misc/freemind , which does not work with JDK 1.8 and jibx-1.2.6-r1 .
Kindly update JIBX to the latest available version in the Portage tree.