The enharmonic spelling - i.e Eb being the same note as D# on the keyboard - is conventionally based on the key of the song, rather than the chord. Enharmonic spelling convention also comes into play to ease the reading of a melody line - i.e it is more logical for musicians to read G->G#->A rather than G->Ab->A - even though the notes are audibly the same.

Band-in-a-Box gives you the option to view your notation in a way that best works for you! Attached below is an explanation of the "Use chord scale for enharmonics" function found in | Options | Preferences | Notation |.

Use chord scale for enharmonics - If enabled, note accidentals will be based on chord scales rather than the key of the song. For example, in the key of Eb, an Eb note will appear as a D# over a B7 chord. This is because B7 inplies the E major scale which uses D# instead of Eb.

Hope this helps clarify!

Best,

Jerry