from the diff of it I would think libyui's ABI changed (there were 2 virtual functions added), but the soname didn't change and the libyui backends don't require the exact release of libyui they were compiled with. As a result libyui-qt wasn't recompiled and is now accessing the wrong virtual functions. libyui-ncurses in return was submitted together with libyui and as such was recompiled against libyui.