Hi again, RM,
I've noticed that enharmonic keys such as F# and Gb can sometimes give mixed results. Whether or not it's tied into the chords used in the bar, I do not know.
For example, in your song in Gb, you have an A7 chord in bar 2. In the diatonic scale of Gb (that is, Gb, Ab, Bb, etc.), the note A is a sharpened 2nd (compare the note D# in the key of C). A chord based on the sharpened 2nd of a scale is extremely unusual to use for harmony purposes. What is much more usual is a chord based on the flattened 3rd of the scale (i.e. Eb in the key of C). Part of the reason for this is that the flattened 3rd exists in some of the prominent forms of the family of C scales. I mention this because it might be that this is part of the logic behind BIAB; I'm not sure, though.
When transposing for sax, what I do is to ask myself what my transposition would be in the key of C. In your case, when you transposed from E to Gb (to get a full tone), from the perspective of C, this is equivalent to going from C to Ebb. When I realized that, it was easy to see that Ebb should really be its enharmonmic equivalent, D.
In the image below, I have highlighted an option that might be worth trying. You should exit and restart BIAB to get the change to take affect if you decide to try it out. Also, you can see that just above the highlighted area is another place for transpose options. You can find this under
Opt | Preferences | Notation OptionsRegards,
Noel