Sorry if this problem has a pretty obvious solution, but I only recently started using Blender, and I can't figure out why this is happening. I have an edge, which I separated into 2 edges (they also have a vertex separating them). However, whenever I try to dissolve only one of those 2 edges, the other one goes with it as well.
Before I dissolve an edge:
After I dissolve the bottom left vertical edge: