I'm directing this at Mavia who was conversing with me about having one thread untwist when railroading upon loop starting (two different ends of the thread used at the same time in a stitch).
I did some more experimenting, both with floss and pearl cotton. You can see pearl cotton's results much more readily. Here's what I discovered:
If you don't keep the threads side-by-side as you pull the needle through and begin the next stitch, one thread can have a tendency to move its position (if it was on the right, it moves to the left) and THAT untwists the thread. It's not the act of railroading per se. It's maintaining the threads parallel throughout the process of stitching.
This phenomena will happen whether or not you loop start. Perfect stitching requires some fussiness on the part of the needleworker. Ask me. I just ripped out some closed blanket because I wasn't paying attention and the threads were coming untwisted, changing the look as the embroidery progressed. I know better. I just wasn't paying attention. I'd prefer to blame it on light conditions. :-) I'm really fighting the issue of having to use a secondary light source. Very bummed about it.
Dianne