building one structure over 2 sims

I have 2 lots right next to each other in different sims which I use as sort of a home base to build on. And, seeing as they're in 2 different sims, the land can't be joined. I've noticed a few funky things happen when I'm building one structure over the 2 lots. A couple of prims have gone missing, sometimes I fall through my floors. Although this could be because I'm overlapping onto linden land a bit. Not sure.

Can anyone tell me what I should look out for while I'm building given my set up?

tks.

Building on the edge of two sim is a litle tricky. when possible I recommend to avoid creating house that that will overlap the demarcation line. Your falling problem is a common problem and can be solve by duplicating the prims to have 2 copy on each sim, This problem is related to the fact that SL software evaluate collision detection only for the prims of the sim you currently active. So, you build a floor on each sim that overlap each other, and you stop falling.

But again, the best solution is to place a seperation (like a wall) on the demarcation line to avoid all this kind of glitch.