Developing a "straight back" pull

I use a drill where you simply hold the empty gun out on a white wall, align the sights, and with hammer down, or safety on, pull the trigger against the stop until I've got a bit more than the force that would drop the hammer, and then release; working on using the information that the sights are giving me to train the finger to move in such a way (straight back) that the front and rear stay in alignment.  When I "release" the trigger, the sights usually move out of alignment a bit.  I guess every tendon and muscle is now working opposite?  How important is it that this release be developed so that it also results in maintaining alignment?  
Thanks.

If I understand right, "release" means the trigger is moving forward and resetting the hammer and sear. If that's true, then it may not matter. I, and I think most shooters, reset the trigger during recoil, so the gun is already moving all over the place. But I know at least on shooter who resets the trigger after coming back to the target. He resets and pulls the trigger in one movement. In that case, it probably matters a lot more, or at least it matters if the movement is large or inconsistent. If it always moves out and back into the center the same way then it can probably work.

You’re not shooting when you’re resetting the trigger, so wiggles and movement during the reset mean absolutely nothing. That should be happening during the recoil recovery; there’s plenty of movement occurring already.

I am just asking in case muscle memory when"extending" the trigger finger after the squeeze, if not given the same attention as when I am pulling,  can impede development of the muscle memory that is focused on developing a straight back pull.  It sounds like you guys are saying that it doesn't matter, while doing the drill, what the sights are doing when I'm releasing?  Kind of like whether it matters when a golfer takes a practice stroke before making a putt, how he brings the putter back to the starting position.  
Thanks much.

This isn't golf.  There is no stroke.  There is no backswing.  A stroke is a full-body movement that takes total body coordination and mechanics.  

The goal with a pistol is to squeeze the trigger until it breaks without disturbing the aligned sights.  The perceivable moments after the shot mean nothing to the bullet on its way downrange.  

Shooting the .45 is very different from air pistol, free pistol, and flintlocks.  The gun will be recoiling and cycling immediately.  You can't duplicate that experience or feeling in dryfire.  How "straight" you reset the trigger is irrelevant; just hold onto the pistol without changing your grip pressure.  You need to be watching for the sights to return to zero and prepping another straight squeeze back.

I think the release is very important.  We have heard of "steering the sights" with the trigger.  On the other side of that coin, I trigger to not UN-steer the sights.  Drills like pumping the trigger before the shot or in dryfire are very important to learn the relation of sights and trigger

I may have misunderstood your original intent of the question. I admit there may be some benefit from improving control of the trigger finger in both directions. I don't think it's necessary to train for the release, but I suspect all training that involves moving the trigger finger while maintaining good sight alignment is a good thing. 

I certainly can't see any harm in pumping the trigger as training.

Thanks Steve. That’s exactly what I was asking about since, when pumping the trigger we have two options; 1) keep sights aligned when squeezing and disregard what you see when releasing, and 2) keeping sights aligned while trigger is moving in BOTH directions.
 I don’t know enough about how the nervous system and muscle memory works.  If I’m creating “more permanent” movements by doing 2, or even “unlearning” good trigger finger movement by doing 1, I’d like to know.

A conscious press and a conscious release is not what we want.  The idea of pumping the trigger is a test to see that the press is straight back and that reversing of the press is straight forward.   I think the subconscious press will show aligned sights throughout.  While a conscious press may not.  Long ago Zins agreed with my saying "you tell your subconscious what you want.  Then let it become part of the shot flow

Make that "show" your subconscious...