Then that is the reason, as dynamic entities they will be subject to the physics engine so if the collision boxes are overlapping they will be forced apart. Unless you need them to move as part of your game you should make them static, if you do need them to be dynamic you will have to very carefully place them so they aren't touching each other.
(You could also set isimmobile=yes but static is better for performance)
Been there, done that, got all the T-Shirts!
