If it's a habit, you just do it unconsciously most of the time, the reason behind it is not important, whether the shuttle is new or not. I'm pretty sure all Lin Dan's opponents, not least LCW, and all the court officials, umpires, service and linejudges and everyone watching on site and on TV know better.
I feel like saying the OP's thread is inappropriately phrased. Whatever his motive, he could have asked:" Is Lin Dan tipping the shuttle and, if so, is it allowed?" Instead , his implication is so negative and unnecessarily provocative (unintended?). To further imply that Lin Dan did it so many times without being caught by all the expert eyes is even more preposterous.
I was thinking, even if anybody tried to tamper with the shuttle, how do you control its flight and how do you know what shot your opponent is going to play and take advantage of it? Besides, getting caught "tipping the shuttle" just once or twice and duly punished is deterrence enough, who can be doing it time after time unnoticed?
Thanks for the reply, I am aware that my phrasing was not too good for my question. I did not want to start any sort of argument for which player is better and also did not want to talk so negatively of Lin Dan. Next time I'll be careful of my wording