Gremlins in the building system?

I have noticed a couple of odd things in the building system, but I am not entirely certain what is going on.

First I constructed a long wall, a sort of garden wall, and then selected and rotated the thing to go along another side of the same plot. Each section of this wall was made from three pieces, each of which had been rotated in one way or another. The first wasll was carefully aligned with the road and the straight side of the ground tiles. After rotation, however the new wall ould not line up properly with the ground tiles and was turned very slightly of of the true line. It could not be rotated as a unit back to square and adjusting the individual sections did not work because they would not quite line up.

I have had the same thing happen with other situations in which I constructed large sections from smaller ones (a starway, for example) only to find that the parts of the original were not properly aligned after selecting and rotating the unit.

Second, I set up a series of transparent panels, each with the same image on it, as in the illustration of the gallery with the fish images, and carefully aligned the panels sothat they were perfectly aligned and seemless. I went away to do something else and when I returned, having done nothing to the arrangement, I found that many of the panels now had small overlaps and/or gaps. I fixed them, but have not yet checked back to find out if they have shifted again. I am quite certain that the origianl arrangement was correct and that the new arrangement was slightly off and that the repairs were not as precise as the original.

Since this is all a web of numbers to some arbitrary precision, can anyone tell me if this is reasonable behavior for the elements of a build? I find this is mostly a problem working with groups of rotated elements that I wish to rotate again so it seems that the most likely explaination may have to do with some confusion or cumulative error since eachof these objects seems to retain it's original object coordinate system. The next question is, of course, is there anything you can do about it? Are fine adjustments necessary from time to time as a build grows or with time?

I tried a shap to grid system, but the grid seemed to be too course for what I was trying to do and, anyway, the whole system imples some sort of grid, the dimensions of which are one click, so to speak.

Comments or suggestions would be appreciated.