I downloaded the Akai manual for the MPC 1000. Pages 61 to 62 have the following:

Pressing the [WINDOW] key in the Pgm field brings up the Program window. In the Program window, you can edit the setting for the selected program.

You can switch the programs assigned to a track within the sequence by setting the program change numbers in each program. You do not have to set the program change numbers if you do not need to switch the programs .

If a track has a program change event with the same number set in this field, the MPC1000 switches the program at the event while playing back the sequence. If you do not wish to switch the program during the playback, set this field to OFF.

Did you set that field to ‘OFF’?