It's because the X and Y axis (horizontal ones for left/right and forward/backwards) won't rotate with the object. So if you rotate an object to an angle that isn't tangent to X or Y, and want to put more objects beside them you need to alter both X and Y. This problem is intensified when the true location of the object is the center of it. If you remain tangent to either X or Y, you'll be fine.
That happened to me yesterday while forging on my "map". I made it so that it rotated in 30 degrees to the left on the X Axis. But then when I tried to make it turn foward on the Y Axis, it turned into some weird ass angle. I though that this only happened to me because I was messing with the settings. On the bright side, I saved myself from being one of those who makes a thread similar to another one, just by taking a minute or two to search around ^_^.
Has anyone figured out a way to get around this problem. Someone had mentioned to rotate by 5 instead of 45. I tried this last night, and I believe the problem is still the same just on a small scale. Perhaps we should try nudging with the coordinating system with the snap rotation off. Maybe by nudging one point at a time could get it right.