Hi and welcome to the forum!
I have seen this many times in my game and I believe it is not a bug, but that it has to do with the centering of the lot.
You say everything is moved. And that is probably just a little bit right? As if off center?
I think this is because you used a 64x64 to place an 50x50. I think the game wants to center it, but that is not possible in this case. Of the 64x64, will be 7 left on each side of the 50x50 and that is an odd number.
So or you could try to delete the 64x64 completely and place an empty 50x50 for your house. (beware that sometimes it is hard/impossible to place a lot back, so make a backup/save first just in case you want the lot back and can't place it anymore).
Or you move the painted dirt etc a little bit to match the new lot. I have done this numerous times and it isn't as hard as you might think at first.
Good luck!