When I destroyed my rocket and rebuild it once again the rocket disappeared from the list. I have to restart the game to have a chance choose my rocket.
P. S. Sorry for my English, I hope I'm making myself clear.
Steps to Reproduce
1st image. You can see the rocket. 2nd image. I have destroyed the command capsule. 3rd image. I rebuilt the command capsule and the rocket never showed again in the list.
This issue has not been confirmed by a developer yet.