Attempting to move Vertices in 2.80 creates new ones instead I have a model that is basically a cylinder.

Several vertices on the top are slightly raised, creating a 'bump' which I want to get rid of.

I've tried using Slide (Shift-V) to move them, and setting the position numerically (N), both individually and with several grouped, and either nothing happens at all, or it creates new vertices instead of moving the old one.

In the below screenshot, I selected every vertex on the top, then pressed S, Z, 0 which my Googling said would set them all to the exact same height. Again, it created new vertices (at the correct height) but didn't change the ones that are incorrect that I'm trying to move.



(Not very easy to see, sorry, but if you open the image full-size in a new tab you can see the new yellow selected vertices below the ones I want to move)

Clearly I am a complete noob when it comes to 3D modelling, still struggling with some of the basics, but this one has me completely stumped.

I don't know if this is significant or not (see noob above), but the lines connecting those vertices are black, while the lines connecting the other vertices around the top are grey.
Had a sudden flash of inspiration... there were multiple vertices on the same spot!

After selecting them all and doing S, Z, 0 I then selected what looked to be the old unmoved ones as well, and did S, Z, 0 again. And then added the 'unmoved' ones to the selection again and did S, Z, 0 yet again.

At that point, it became clear that that was the issue.



A couple more rounds, and the 'bump' is finally gone!



Wish I'd thought of that before bothering you all, but hopefully this'll help someone else in the same boat!