I came across some interesting facts, recently. You know how each character has an image album?
Well, Syaoran's includes a track with Sakura and him chatting. In one point in the conversation, they get on the subject of their parents. From here on I'll quote. Forgive me if my translating is a bit off:
Sakura: So what about your parents?
Syaoran: I used to see my dad a lot when I was young, but...
Sakura: I'd love to meet your dad!
Syaoran: My dad...died when I was a small boy.
Sakura: I'm sorry.
Syaoran: It's ok.
Sakura: I'm really sorry, but I guess we're the same...
Syaoran: About what?
Sakura: Apparently I used to see my mom a lot, but she died when I was so young I don't really know.
Syaoran: So that's how it is...
Sakura: But! But! We have a lot of pictures of her! Do you too, Li-Kun?
Syaoran: Nope!
Sakura: Howcome?
Syaoran: Well, because of various things...
Sakura: Hooeee?
So, something happened that made Syaoran never get to see pics of his dad. I don't know if that means Yelan was bitter toward him or what, but something went on.