Missing Green Mug Reflection

A photorealistic studio shot. On a wooden table sits a solid red cube. Resting exactly on top of the red cube is a glowing yellow sphere. Directly to the left of the red cube is a green ceramic coffee mug. Directly behind the red cube is a tall, ornate silver candlestick. Behind all of these objects is a large, clear mirror reflecting the scene. In the mirror's reflection, the red cube, the yellow sphere, and the silver candlestick are perfectly reflected, but the green ceramic coffee mug is completely absent from the reflection. The space where the green mug should be in the mirror shows only the empty wooden table.