I'm not even sure this is actually considerable a bug, but when I fished up a Peisteskin Map the other day, since I already had one in my inventory, the game dropped it.
However, I got the 18h CD anyway (or at least, I think so, since after 50 times I tried to get it again, I couldn't: fishing is really uncertain on checking theories).

However, it's my fault for not putting the first map with a retainer, but is there a good reason for that item to be "Unique"?
Same as Phoenix Down, I don't really get it.
With Phoenix Down, actually, it's even funnier. Quests gives you 4 of them, sidequest in 2.1 adds a fifth one.
Thus, even distributing them amongst your retainer, you can't keep more than 3 of them at the same time!

Then what's the point with the map being Unique? You don't want a player to have more than one at the time? Then why you let me have three, with retainers? Or why can I keep one of each kind, but not two of the same?

Like I said in the beginning, I'm not sure if mine is a bug report or a complaint, so sorry for putting it here if it's the wrong place!
However, if fishing up and auto-dropping give you the 18h CD, please fix that: the moment the game drop away the map, it's pretty obvious I didn't get it.