May not have been very clear in there. Someone I know claims not to be aware that they are the joint owner of a property even though they are listed as joint owner on the Land registry title deeds. It's not that the house has had a new mortgage taken out on it. It was only purchased, presumably with part of the purchase price covered by the mortgage, in September last year.
It is very difficult for someone to not know they joint-own a property as they would have had to sign a lot of paperwork when the property was purchased or transferred so it sounds a bit odd!