Vanishing upgraded ship

And p.s., The first time I saw this, I figured I musta missed something. The second time, I remembered the first time and began to suspect something was amiss. The third time I wrote a song about it. Wanna hear it? Here it go...

Maybe in the confusion of upgrade/downgrade/de-feet/re-fleet ...
Pirates stole that ship ?????
More likely the corrupt Alpha Krappa Corp sold the ship for scrap ....
And now are charging you at a 50% interest rate for the upgrade you don't have !!!!

The real answer:

Magic

Hmm...sounds like it failed to create the graphic for the ship when you de-fleeted it...maybe it still considered it to be not on the map when it went to update the image. 

I'll try to repeat it with a custom-named ship, and watch the ship list.

Edit:Eh, won't show up on demand; a finicky little phantom.
I'll do quicksaves whenever I have the opportunity to upgrade a fleet member.

...And I'm gonna have to rename the next planet I invade Alpha Krappa Corp.

Ok, I got a repeatable version of the problem, captured in this zipped save game.

In the upper right of the map, there is an orange fleet called "Trouble", containing two vessels, 'Outlander', and 'Gwinavere'.

Choose 'Outlander', go to it's details and upgrade to a 'DD Guideon-1103'. Then de-fleet the upgrading ship. It will disappear from the game.

Something that may be worth noting is that as soon as it's upgrading (but before de-fleeting it), the hit points are negative. Also, the single remaining ship won't move for a week, as though it's somehow tied to the upgrading-for-a-week process.

Also, an entry appears in the ship list for the upgraded Guideon class destroyer 'Outlander', but there doesn't seem to be a ship on the map that it corresponds to. Centers on the square the fleet was on, but no ship.

Hope that helps.