Oh, this is so similar to two bugs I encountered on the Wii U. The first time was when I used my bug net, and a Snail spawned. I ended up catching like 800 something Snails.Tbh I don't think these qualify as "bugs" but there was one bug that I encountered but it was actually hilarious
So if you had a hardy shell on the PS3 edition, summoning the mount would spawn a frog next to it. Literally infinite froggies xD
The second time was when I tried placing an Ultrabright Torch in the air by accident, and it turned into a firefly. I ended up sacrificing like half my stack of the torches to get fireflies.
Never reproduced either, sadly.