My whole fleet of constructors going almost across the whole galaxy(I'm top right) to build stuff in a system I haven't even explored, next to several enemies instead of building closer to home(or just sitting on their ass doing nothing instead of provoking wars):

This has ruined every single game for me along with explorers deciding to explore on the other side of the galaxy instead of neighboring systems.
At least I see 1.0.9 fixed nebula logic so I don't have to watch my entire transport fleet fly straight into one and get stuck.
