created a dev game (and even got replies to it from folks who didn't join) and later, when I check the progress of the game, it's not to be found, no matter how I filter my games list.

Which board was it on? Ideally boardid if you have it. I'll try and track it down.

Sure Tom - main board is 5836, I believe the particular scenario is 5839.

I've searched the database and can't find any hidden games. The last game that you had joined and / or played in was http://www.wargear.net/games/view/526415 which ended normally.

The game in question could have fallen foul of the housekeeping script which deletes games that have been open for > 30 days.

No, it couldn't have been the 30 day rule - it disappeared on the same day it was created.

It's also not the first time this has happened.  It's occurred probably 3 or 4 times over the years.  It's not a big deal, however, and if it requires a lot of digging, than I would suggest it's not worth looking into.  I was able to create another game.  I was just a bit curious as to why it was happening.  

Ok, for troubleshooting purposes I should relate what happened when I did not accept the invite, which is  why I replied to Thingol via PM. Immediately after choosing to not accept the invite, my tab crashed before I could offer my reason in the message box. Upon attempting to return to the page via my browser history, instantly told me this game did not exist. So, I guess I broke it  ;)  Not sure if this helps, but I found this rather odd.

I would rather say that the game broke when you were declining it hootz, not that you broke it.