Why do Asian girls always hit on my boyfriend?

I'm a a Caucasian female and my boyfriend is also Caucasian as well. Girls are always flirting with him because he is attractive and I understand that since I've been flirted with as well while in our relationship, and he'll tell me whenever they do it and we'll laugh it off, no big deal, fine. But for some reason when we're out together, Asian girls will shamelessly flirt with him right in front of me. This has happened 8 different times with 8 different Asian girls and I don't get jealous, I just feel kind of disrespected since when we're together it's pretty clear we're a couple. This one girl today at our mutual friend's house GRABBED his phone from his hand and saved her number, told him to text her about hanging out "one on one" and grabbed his knee. I was shocked because this same girl has always been very reserved and shy when I've seen her with just other girls and myself, but all of the sudden she is ogling him. She didn't even say hello to me or acknowledge my presence at all, and this is the same type of situation that has happened with the other Asian girls hitting on him in the past.I'm not racist by any means, I'm just wondering if there's a reason this has happened to all be Asian girls and if other Asian girls think this type of behavior is socially acceptable, because I find it downright rude.