To come back on this, I've sometimes worked with singers who have perfect pitch but limited knowledge of harmony. Although such singers almost never sing out of tune (as such), they do sometimes sing wrong notes. That's a bit like striking the wrong note on a piano, they tell me, as it's ‘in tune’ although wrong. Intervals such as G

to B

seem to be of the sort which could result in just such a wrong note.
There are certainly singers who will understand the harmony behind these early Berg songs, but there are surely others capable of singing them effectively who might not. This is also the vocal score for the orchestral version which introduces colours to which the singer needs to respond.
Anyway, all that aside, it is good to know what is behind this perhaps (or perhaps not) slightly disconcerting notation.