Please have a look at
Commenting the line in /etc/java-8-openjdk/accessibility.properties may
help with X11 issues, but I believe the ground issue is that the openjdk
awt toolkit doesn't tell X11 that it is using threads, and thus all
kinds of race conditions can happen within libxcb etc. just because
freemind happens to be using threads.
This is the maintainer address of Debian's Java team
debian-j...@lists.debian.org for discussions and questions.