Sounds like you only string one racket. Get a space and put it between the post so the mounts can't move. When adjusting the posts maybe pulling from the bottom and holding them there until you tighten them would help. This would enable you to pre-load the mounts.
Everyone has the right to be stupid... it's just that some people abuse the privilege...
Balance - 31.0 cm, Weight - 358 g, SW - 346 Kgcm^2