You have a point: since there is no unified libertarian manifesto (not all subscribe to the von Mises one), one cannot tell; individual prominent libertarians (self-professed) seem all over the place on such matters. For example, the United Kingdom Independence Party calls itself libertarian, but while opposing gay marriage on the religious plane, it supports gay civil unions.
I have seen self-described “libertarians” even go so far as to oppose age of consent laws on sex as well as oppose laws against incest.