Customer account on Sales order header and line is not the same

Hi there,

Is anybody ever faced that when create Sales order, header and line got difference customer account?

I found a transaction that user created Sales order header with customer account A, then change to customer account B. (not yet create any sales lines)

Create sales line and found that on Sales lines was customer account A (actually it should be account B).

I tried to re-produce, but couldn't get the same as User. 

Could anyone pls advise what should we protect or what should we do.  Thank you.