Yes, I'm sure.
Here is the thread where the rule was first explained to me, by someone who should know:
http://webdiplomacy.net/forum.php?
threadID=364994#364994
Because of this, I don't think that it's a bug; I think that it's intentional. (I leave open the possibility that this was changed in the 0.9 upgrade, however.)
Here is the game in which it happened:
http://webdiplomacy.net/board.php?
gameID=8216France made the Autumn 1904 moves, missed the Autumn 1904 retreats, and immediately went CD.
Of course, there's no record of that now, but for corroborating evidence, here is the forum post where I recruited a replacement:
http://webdiplomacy.net/forum.php?
threadID=374653#374653
The situation described there matches the game only at the end of Autumn 1904.