The first demo shows the leaking, the rest shows it does not happen in pure or under any circumstances in vanilla quake 3. As you can see the leaking only happens when moving and jumping while shooting, standing still it stays in crosshair.This is a freshly compiled ioquake 1.36. Does this happen on your system too? I can’t use pure server since I need unpure for my mod to work correctly.
I will add that I was debugging an issue with my mod earlier, and I found that none of the changes I was making to a file were being applied unless the server was unpure. I imagine this could be the same so a change that was made in official ioquake that broke unpure lg went under the radar because testing only occured in pure server?