Extraction/ejection problems on S&W 4006

I have an S&W 4006, .40 cal. Usually once every other magazine, a cartirdge will fire, the slide will cycle, and bring up a new cartridge. However, the old, spent cartridge does not eject, and the pistol ends up jamming, as the new cartridge jams up against the old cartridge, and jams it back into the chamber. I have replaced the magazine springs (actually I bought a full set of springs from wolff, but only got around to the magazines), but still the same problem.

Is this an extractor issue or an ejector issue? How can you tell? Thanks!