hmmm... I just went back to the same song I've been experimenting with all day... this time I hilited the track and consolidated the audio region first.

After tempo mapping (actually I didn't adjust any tempos, I just set bar 1 and sent it back to RB) I answered with the first option and it still truncated the audio at the same place it has all day.

All else being the same, choosing the default answer didn't truncate.