This is a fault in the scheme used by the renderer to manipulate and display adjacent sectors. It is intrinsic to game design.
This fault is related to the above bug. Since it too is based on the intrinsic way the renderer treats adjacent sectors, it is also ...
This isn't the renderer, it's the engine. We just need to optimize more.
FIX IN PROGRESS.
For speed, Nether relies on the hardware scaling system. Since there are only two sprite sizes, popping is inevitable. This is a hardware problem.