Olivetti Lettera 22 skipping spaces

I have an Underwood-Olivetti Lettera 22 that hiccups occasionally...When I'm typing along like normal, it has a tendency to add spaces after certain letters without me having hit the space bar. It's almost exclusively with the letters around the edges, and especially with the P, O, D, and E keys. I looked underneath and it looked as if some of the key levers were a little loose, but I'm not sure. It sits on a very level surface, so I know that's not the issue.