I think you got too hung up on my Ireland example, which on reflection I shouldn't have included because it's not relevant. The Bangladeshi government have confirmed that she is not a citizen. She has been stripped of her British citizenship because the British courts believe she is eligible for...
She's apparently not a Bangladeshi citizen, she's just eligible for citizenship (in much the same way I could apply for an Irish passport if I wanted to). That's what's so insidious about this - it means anyone with a foreign grandparent now has a diminished, second-class form of British...