I happened upon this bug by accident, but was able to reproduce it:

(This should all happen on the same turn)
1. Purchase a ship at a planet.
2. Go to the "Shipyard" screen, and obsolete the ship design you just purchased (I didn't decommission any, not sure if it matters).
3. Optional?- Design a new ship, preferably one more expensive than the ship you just purchased in Step 1, if needed.
4. Go back to the planet where you purchased a ship in Step 1, and set it to build a ship more expensive than the one you had purchased (when I tested, it was my newly design ship).
5. The planet will then redirect the purchased progress from the old ship to the new one, then work on the ship until it says "0 turns remaining," but the ship will never actually complete (be put into play). Neither will any other ship you ever try to build there.

From that point on, for the rest of the game, that planet will never be able to build a ship. I tried switching production, setting it to produce "Nothing" then switching to another ship, quitting GC2 and coming back, even simply decommissioning the Starport and building a new one. Nothing, the planet will never produce again (which was kind of a big blow in a "Duel" game with only 8 planets total ).

Bug Unknowns:
-Can the bug be reproduced if you switch production to a cheaper ship after obsoleting the old ship design.
-Is it neccessary to design a new ship in the meantime.