I use StyleMagic software to do this work, and the length of the Intro1 shows correct on the keyboard. But only drum tracks are heard. Then I found that:
"copy MAIN-C (2 bars) to INTRO1, then edit INTRO1 on the keyboard (by playing a bass line). This works, I have a two bar INTRO1 that plays the bass line as I wanted"
No idea why. So I figure out that I had to create main-A for example from a MIDI file, then onboard, copy main-A to Intro1 (after adjusting its length to match with main-A length. Then copy main-A back from the original style.
Cumbersome but this works.