Ship Designs disappearing between turns in PBW game

This has now happened several times to me, however in the past I've attributed the behaviour to some glitch in upgrading the PBW game to the latest patched version. Most recently however, there has been nothing out of the ordinary that should have caused it to happen - at least that I can think of.

The symptom is this. I create a ship design, and add it to several constructions queues. The ETA is usually at least two turns. I 'End Turn' and submit my turn file as per usual to PBW, and when I go to play my next turn everything seems normal - all of my ships are following their orders, research is going along as it should be, etc. However when I go to add my new ship design to a few more construction queues, I suddenly discover that it doesn't exist any more as it is not listed in the Ship Designs window (neither is it listed as 'Obsolete'). When I check all the construction queues that I filled up last turn, I now find they are all empty - or if I added several different designs, they are at least all missing this new ship design from their queues.

I don't have any reasonable explanation for this behaviour. I am certain that I *did* create these designs, and that after creating the designs I either saved the game or Ended my Turn properly. The only possibility I can conceive of is some problem with saving a game in the middle of a simultaneous-mode turn. Often, I won't have time to sit down and play a turn from start to finish, so in between sittings I will save the game, over-writing the same gamefile I had loaded. I also make it a habit of saving the game after I have completed my turn, but immediately before I hit 'End Turn'. That way, if I want to review what I did while waiting for others to submit their turn files to PBW, I can just load up the save game and poke around.

Has anyone else experienced anything similar, particularly with simultaneous/PBW games? I'm especially curious if this has anything to do with saving the game in the middle of your turn. Any help or suggestions are more than welcome. This is a real pain when you finally research that new Ice Colony module, and excitedly add your new Ice Colonizer to 5 or 10 queues throughout your empire, only to find on your next turn that suddenly the design doesn't exist any more..