You appeal to be relying on spellcheck too much.
What you are noticing is no doubt the effect of unlagged (lag correction code).
or perhaps the distance between the alien and yourself is not correct.
That's pretty much it. You think you are round a corner and they are on the other side, but to them you are still in range to be killed. This is because of the lag between each of you and the server coupled with the fact that unlagged allows you to hit them where
you see them rather than where the server sees them.
Also note that this is more of a complaint against lag correction than unlagged in particular. Unlagged I believe DOES have issues but this is more debatable.
EDIT: Also this is the wrong area of the forums to be posting this in. Feedback or possibly even general discussion are appropriate.