ProBuilder: Extra faces being created

I'm using ProBuilder Advanvced 2.9.8f3 with Unity 2017.3.1p1

Extra faces keep getting added on top of existing faces. I'm not sure what's causing this to happen. When I find the extra faces, I delete them with backspace. After making edits, often more extra faces are added. They show up even in places where I wasn't editing.

The type of thing I'm doing is editing using 'Connect Edges', welding or collapsing vertices, dragging materials on faces and using the UV Editor.

Usually I notice the extra faces when I try to change the material by dragging it onto the face, but the material doesn't change. Then I hit backspace and it gives a 'Delete 1 Faces' message. When there is only one face it allows me to change the material.

Is this a bug, or is there a hotkey for duplicating faces I'm hitting by accident? Also, this doesn't seem to be the objects being accidentally duplicated on top of each other, as I checked for that by moving the object.

 

Thanks for replying. I think it might actually be that I duplicated the object and only thought I had moved it to check if it was duplicated. I could have sworn I had many duplicate faces that hadn't come from accidentally duplicating the object, but I may have gotten confused at some point. I went back to the project I was working on and found extra faces, and the object had been duplicated, so I think this probably is what's causing it, or maybe as you suggest above. I use Ctrl-S to save the scene, so probably have been hitting Ctrl-D by mistake.

I had tried Unity 2018.1, but the WASD keys were broken, I think ProBuilder was using some of the keys preventing WASD flythrough from working.