FarmVille Community Manager Stumpgrinder has been on the case, addressing these issues over on the official FarmVille forums. For users that have expanded their Duck Pond once and then can't look inside the Duck Pond, Zynga is currently working on releasing a patch.
As for the second Duck Pond that many users are reporting appearing in your inventory, Stumpgrinder says that yes, you can in fact use this Duck Pond as normal. In fact, Zynga is encouraging it, and the double Duck Pond issue "should be ok" for users, meaning that you shouldn't receive an out of sync notice when trying to build it. Stumpgrinder never did clarify as to whether or not the second Duck Pond was an intentional release, or whether it was just a glitch that Zynga decided to run with, but I suppose we'll take extra Duck storage either way.
After being forced to remove the Duck Pond expansion when it was first released due to issues, it's unfortunate that Zynga still hasn't patched all of the bugs with this second release, but I suppose while we're waiting for Zynga to fix them, we can always build our second Duck Pond. Who's with me?
Did you start building your second Duck Pond, or did you delete it for fear of it being removed from your game? Let us know in the comments.