Ed:

Let me see if I understand this situation correctly.
Here's what I did as a test. (My default Chord Display Type is set to Standard)

- started with a blank, new BIAB song/grid sheet
- in the first 4 bars, I entered: | C | F | G7 | C |
- I then copied those 4 bars to the next 4 bars, i.e. 5 through 8
- I highlighted ONLY bars 5-8 & selected Edit > Transpose > Transpose From .. To
- Left Transpose From Bar set to 5, and Num. Bars to Transpose to 4
- Left Tanspose From Key at C and changed Transpose To to read D
- That changed Bars 5-8 to show: | D | G | A7 | D |
- Selected the Chord Display dropdown and set "Choose type of Chord Display"
to "Roman Numeral"

The grid now shows bars 1-8 as | I | IV | V7 | I | and | II | V | VI7 | II |
which is what I would expect.

When I play the song, it indeed plays the first 4 bars in C, the next 4 in D.

I'm just wondering what you were expecting.
In your case, would you want bars 5-8 to also DISPLAY as I, IV, V7, I but PLAY in the key of D, that is transposed up 2 semi tones but noted as if it were still the primary key?

That would make sense if you're trying to practice a song in different keys, but still have each key notated as if it were the primary key.

If that's the case, then (I suppose) your Wish List item would be:
"I want to select any bars and have them DISPLAY in one key (say the original primary key) but SOUND in a different key of my choosing."

Perhaps that would only apply if you were using Roman Numeral or another non-standard display.

Not sure what instrument you're practicing on but you may want to check out BIAB's "Capo" feature in the Guitar Window. I believe there is also provision for horn players to display in one key but sound in another.

Good luck!
LLOYD S