I have a 590 that I used for the first time only a couple of weeks ago. It's been sitting around waiting for a while. I didn't try what you described, but the fewest number of shells that I loaded were three. I had no feeding problems at all. I did do some rapid fire with all nine shells a couple of time and it was great. I think once I got rolling it used me.
Sort of like a little kid walking a big dog.
No stange new gun clitches at all.I'd call mossberg.