Empty beacons (no modules inside) count towards beacon efficiency calculation, so placing a empty beacon will make other beacons have less impact.

I am sorry, I didn't confirm the reason of why you can get stuck.

When you place a underground/normal pipe then the collision box of the pipes next to it changes so there is no gap between pipes. Because you can place a underground pipe under your feet you can expand collsion box of a pipe into ...

Version: Build 82066 expansion, win64

If you walk till the edge of a pipe, it is still possible to place a underground pipe under your feet then you can get stuck inside the underground. I tested for many directions and it works in every direction. I guess that is propably because from what I see ...