Why is my quick selection changing after I release the left click?

The issue is very hard to see but the Vampire has a marquee around it in both screenshots, but the marquees differ.

While still holding down left click

Selection after releasing left click

This is doing my head in, I only just found out about this tool, it seemed perfect, but now it keeps doing this. I feel like I checked an option or changed something simple that is screwing it up but I have no idea and google hasn't helped, all the videos I have seen everyone's tool works fine.

I appreciate the assistance :)