Do they run a quicker bus from Burnley to Accrington not via Padiham? If so they may be encouraging people to use that instead.
There is, the 9, but that only runs once an hour, I believe.
Looking at the map, I'd hazard the following guess:
Both the M1 and M2 go to Padiham, then the M1 to Accrington and the M2 to Clitheroe. Passengers for the outer destinations can look for their number (M1 or M2), whilst passengers for Padiham can look at the destination, rather than for both numbers. *
It appears to be a sort of local destination to start with, and then I presume drivers either reset the blinds at a set point, or may eventually, if not already, happen automatically. Seems like a sensible compromise to me.
I have seen running boards from other companies where drivers are instructed at which point on the journey to change the blinds, particularly where journeys run through.
*That said, although Accrington might be close enough not to need a split destination, what about Clitheroe or Keighley? If they do, perhaps the blinds are just always set the same way? What do the M2 blinds look like?