Today, I thought Momo had lost her bat wings. I was very sad about it because she hadn’t even worn them for a full day yet. Then I discovered that she had lost her wings when I had changed her outfit earlier today. Unlike the other potions, the bat wings are removable. When you take them off, they turn into a wing symbol in a circle (see below). My bat wing symbol was stuck behind a tree, but luckily I could grab it. Now Momo has her bat wings back.

Just in case anyone out there thinks they lost their bat wings before the three days of the potion are fully done, look in the last place you changed your pet!
Update – October 14, 2009
It’s sad to read the comments that so many people have lost their wings too.
Many comments mentioned that the bat wings disappeared after being removed and placed in the inventory chest. Since I had only a couple hours left on my bat wings, I tried putting them in my chest to see what would happen. They disappeared as many of you have said. So be careful everyone. Do not take your wings off and put them in your inventory chest because they will disappear, even if the time left on the wings has not expired.
For some reason we can take the wings off, and they can be hung up in a room on a hanger (like other clothing items), so if you’ve lost your wings, it’s worth checking the walls of your house. If you’re missing your wings and can’t find them on the walls, then there’s a chance that you accidentally put them in your chest and they’re gone for good. Also, avoid taking your wings off at a friend’s house because you may never find them again.
Thanks to everyone who posted a comment to share their experiences. You’ve all helped solve the mystery of the missing bat wings.