Thanks for the feedback!
You can't put an item you're holding directly into the trash, you can put it back by clicking again on the "container" you got it from. The trash is for clearing the tray if you've made an order incorrectly or the customer leaves and you need to start a new order.
Oh and I think I just realized what caused the issue with your mouse! The mouse is hidden while holding an ingredient, and then is made visible again when you put the ingredient down, so I'm guessing a day ended while you were holding an ingredient. I'll need to add something that makes the mouse visible upon a level ending to avoid that problem. Thank you again for the feedback, it's been very helpful!