Infinite ro bins

Same with me, but the egg was in the chest. I got sent to the 4th island quite early (at the beginning of my first humid season) and I've decided I don't want to waste time to hatch the egg yet. I put it in the chest and for ten days everything seemed to be fine. I made a little trip to the second island and stayed there for five days, came back and the first thing I saw when I entered my house - a Ro Bin. Okay, I think, this is surprising, but maybe that's how it works now? The shell he's supposed to follow was on the floor, so I picked it up, but it multiplied. Only when I took out the unhatched stone egg from the chest and dropped it on the ground (it disappeared immediately), they stopped duplicating. Now I've got four shells and four Ro Bins - four shells and three Ro Bins are outside, one Ro Bin is inside my house, stuck in the wall. 

I had this same issue, I didn't understand what was causing it (didn't know it was the stone egg I stuck on the shelf) and thought the Ro Bins were falling through my wall. I had about six or eight of them at one time, and like 10 or 12 robin eggs (yes, more eggs than Ro Bins!)

I tried using some of them, but two Robins were apparently linked to one Gizzard, and two others linked to another single Gizzard, meaning I had a bunch of eggs not linked to Ro Bins at all, and I could have two follow me with one Gizzard, or four follow me with two. Also, however, the Robins would randomly disappear on me, then reappear just as randomly, with my loot inside them! I had to stop trying to use them and parked them in the middle of my village. Then, when I'd go back, there would be less or more of them than the last time I was there. They'd also get stuck in walls, or outside the walls of my home. It was a real mess.