I have managed to reproduce this a few times, and since it appears to be reliably reproducible, I hope this is of help.
When building ships, I tend to recycle names for my ship types. If I am playing as a race I already used a given ship name for, I often already have a potential ship type with that name, but one that uses different techs.
If I delete the original ship design, then try to save a new ship type with the same name as the one I just deleted, my game crashes.
