is there any way you can send us a link to your project because I'm still trying to figure out what it is you're doing.
The search zero crossings thing is a toggle choice that is either on or off. It makes sure that whenever you make an edit, that edit point (beginning or end point of a region for example) always falls on a 'zero' amplitude value prevents pops and clicks occurring from sudden changes in amplitude.
If you are trying to edit a sine wave, how did you generate that sine wave. When you are editing it, what exactly is it not doing? Your edit points are either going to fall on a zero crossing (zero amplitude) or not. Nothing should really be 'updating' in logic and even if it does, we're talking a matter of samples here so unless you are zoomed right in on the arrange page I doubt you'd be able to see it anyway?
Does that make sense? Can you post a project folder with files so we can see what you're trying to achieve?