Losing family relationships?

I seem to have noticed a new glitch in my game...

Firstly, I moved my 'daughter' sim out of the family home, and after a bad relationship (who knew he was gay?!) she moved back home. Only, when I moved back home, I found in the 'mother's' relationships a new child that she knew as her daughter, though she didn't appear on the family tree and my 'daughter' sim knew nothing of her and didn't recognise her as her sister when they met. i thought, ha isn't that weird and ignored it.

However, a couple of generations down the line - I now have a man who got married and had a baby. All was fine. Then, I had a save error glitch that I've noticed on here. Got around it by going to manage worlds and it let me save it from there, just not from the lot. Didn't seem to be a problem. Loaded it up again today though - and the mother of this baby has completely lost all relationship with the child and isn't recognising it as her daughter! Pretty frustrating as now it doesn't look like it's her baby at all. And although the dad still recognises her and his daughter, the baby isn't showing on the family tree at all. It's all very strange! 

Anyone got any ideas? I've just tried closing the game and I'm about to reboot it now and see if that's fixed it but doubt it!