Comment # 1 on bug 927718 from Jean Delvare

Got it. libdvdnav_plugin depends on 2 libraries, not one. Switching to
packman's libdvdnav4 wasn't sufficient, I also had to switch to packman's
libdvdread4. After that, DVD navigation works again in VLC.

So it is the same problem as bug #926842 after all, libdvdnav and libdvdread
should have had a soname bump but did not.