Some strings tend to be not exactly vertical/horizontal after playing
For some months now, I string my badminton rackets and friends' ones (about 21 lbs). Everything is fine, except that, during playing, some strings tend to leave the horizontal (or vertical) path. That is, they bend slightly (everybody has already encountered such things when playing badminton).
I'm wondering if I can do something special to avoid this problem (that happens often with other stringers as well).