Comment 8 for bug 1193243

google only finds a bunch of bug reports for "failed to install/upgrade: trying to overwrite shared" but no explanation.

bug 1533780
bug 1574351
bug 1279192
bug 1490282
bug 1290155
bug 1464735
bug 1471677

Could be an issue of a missing "Replaces"-declaration somewhere. Possibly related to multiarch, too. https://bugs.launchpad.net/ubuntu/+source/icedtea-web/+bug/1471677/comments/3 strongly suggests this.