Getting multiple duplicated edges all the time.

Hello. I’m new to Blender and have been learning the ropes with the help of online tutorials such as the ones on CG Cookie. Whenever I work on anything for some strange reason I keep on creating multiple copies of edges and vertices in the same exact location. When I go to delete one of these I’m often finding myself deleting 5 of them in the same exact location. I’m not sure how I could be creating these copies. Perhaps there’s a key that does that and I continue to accidentally hit it.

The most recent example of this was when I was starting to work on a new model. I used the original square. I scaled it, applied a mirror modifier along the x axis with clipping checked and then I extruded a face along the x axis to turn the square into a rectangle (thinking back I probably could have just moved the face, but like I said, I’m still learning the ropes) and went to delete the lines in the middle of the rectangle left over from the square. Well at the location of each of the square edges there were 4 edges, meaning I had to delete the edge in the same place 4 time for it to finally be removed.

Does anyone have any idea how I keep on creating these? Thanks in advance.

If you duplicate (Shift+D) or extrude (E) by accident or extrude and then cancel the extrude (you need to undo not just press Esc) you can still create the duplicate vertices. Select all vertices (A) and remove doubles (W / remove doubles)

It must have been the cancelled extrudes. Thank you so much! This has caused me so much frustration over the days.