Warning: SDC put me on the wrong flight!

I got in to the airport much earlier than expected and looked to try going sooner. At about 0535, the checked-in change flight button offered me all of the options, 0630, 0730, 0900, etc. I picked 0630, which I thought was a bit surprising to have offered, but after a moment it said I was confirmed.

When I looked at my boarding pass, it was actually for the 0730. I checked my screenshots, so I am certain I did not goof with what I selected. I tried again to pick the 0630, and again it re-put me on the 0730, with another email receipt and a new seat assignment.

I suspect the 0630 was under gate control when I was trying to pick it, so SDC couldn't get me onto it. But it should either not show that as an option or give an error and do nothing. It should NOT move me to a flight I didn't pick.