I guess the bamboo floor thing is a bug? Or a feature?
I found out about it a few months ago on this forum. I think it was from a thread about someone who built this garish, purple stonework house that was private and someone asked how they could see the stone blocks.
Basically, if you put a bamboo floor down, you can see anything placed above it without stepping on the plot. The annoying thing is the bamboo floor looks horrid, so I try to cover it up with something. I put the stone floor tiles over it, but you do get these strange little things that pop up. If you look at the polar bear rug on the bottom floor, you'll see dotted lines running through it. That's from the bamboo tiles. Oh, another thing is you can't build anything on the very north and west edges of your plot. You can't place bamboo tiles under that part, so nothing will show up on the upper floors.