步法與重心 may be the cause to the problem
My cousin had a 正手拉波 動作 problem, I told him many times but he could not fix it...
Once we took a lesson together and he was having a match with the teacher
the same problem came up
The teach said it was his 步法 problem that caused the 動作 problem
He used muti-balls to show him and that 動作 problem really happened ONLY when he was not in proper position due to footwork!
^^