The "Custom Button Label Area" (in activity mode) has some restrictions:
1) The commands are re-grouped by device priority. The device in the left column has top priority. The next device (in the next column from left to right) has 2nd priority and so on. Workaround: If you need a command from a lower priority device to be grouped with the ones from a top priority device, simply add a "bogus" (a do nothing) command in the top priority column along the same row (line), or teach the command to the top priority device.
2) A command name can only be used once per column. This restriction applies only within the "Custom Button Label Area". Workaround: Teach the command under a slightly different name.