The yellow outline is usual with elevators... If I recall correctly, it indicates where the elevator piece is on the floor below. It sounds like some sort of glitch, as they should line up for placement. I've never had that problem occur, but I haven't built an elevator for some time.
Have you tried to build an elevator on a different lot or in a different save file. Doing that will determine if the problem is exclusive to that lot or save file or game wide. You said it was an imported house. Sometimes when building cheats are used and not turned off before saving, strange things can happen to the lot. I've never heard of this problem before but I guess there is a possibility that it is due to a cheat being used.