This is normal if they can't calculate the charge immediately: they book you a place on the flight you may wish to change to and you can see it in MMB and even (where otherwise allowable) choose a seat. So you do indeed have two flights appearing, under the same record locator, when clearly they are alternatives and you can't possibly take both. I'm afraid it is also normal for BA never to call you back about it ; there seems to be quite a big hole in BA's systems here and it is pretty disgraceful.

I'm pretty sure they can actually tell that your ticket is for the flight you originally booked and not (yet) the other one, even if this isn't apparent in MMB.

I'd say the chance of your being issued a valid BP for the earlier flight with no manual intervention at this stage is zero. I suppose if you turn up at the airport and play the "confused" card they may change your ticket as a goodwill gesture for their not having called you back to sort out the situation. But I would really recommend calling BA about it. Do you have any clue roughly what the change fee is?