No it's something about the other person gaining rights to live there, so if I were to default on the mortgage, the bank have an agreement with me where they can repossess it, but they don't have an agreement with anyone else who might live there.
When we did our mortage, there was a bit about anyone over 18 having to sign a disclaimer-type letter saying they agree that they don't own any share of the property. Someone I used to work with had to sign one when her mum moved house as well, she got one of us at work to witness it IIRC
Don't they only care if you're charing rent?