Digging Trays

I tried to create a dig tray for Nibbler, so he could find some tasty treats without me just handing them to him or putting them in his treat ball (I'm trying to make him work for them more), but I think I may have confused him. He keeps doing his business in the dig tray, even if his litter tray is clean. Since introducing the dig tray he's also started to poo right next to his litter tray. I know it's not a cleanliness issue making him avoid the tray so I'm wondering if I've just confused the little guy by giving him something that looks very similar to his litter tray. I'm not sure what to do now. Should I keep on top of the dig tray and keep it in his pen so he's got an extra activity, or just remove it because it's making him poop outside of his litter tray? Or am I being silly and it's perfectly normal for a bun to poop in their dig tray? It just seems odd I'm wasting so much hay!

Willow always pees and poops in her dig trays (although I make hers up in a big cardboard box as she is a larger bun). I think it's just part of deal that goes with giving buns dig boxes. As long as he gets the concept of it I wouldn't worry too much about confusing him. Buns do like to go to the toilet where they eat, the little charmers