to reproduce:
note that the drop-down selection menu treats it as g indicating the greek language ... an absurd assumption on several levels - gha does not equal g:ha
That's not actually what's happening.
What's happening is that there are no matches for "gha" in your current resource, so it goes looking for a match in the rest of the series, and finds some in the Greek resource. If you don't want this behavior, then you could choose to edit the series in your library for one or both of these books so that they aren't considered in the same series.