I found out that this fix in 16.04 introduced the crash: https://cgit.kde.org/marble.git/commit/?h=Applications/16.04&id=7859bf1cc1fdaf07b70446b1530358bff7bf43e3 Before that, the "Edit Bookmarks" dialog still used DMS if you switched to UTM, and therefore didn't crash. So we could revert this to prevent the crash until it's properly fixed...