Why is my glazed cazuela apparently seeping oil?

I own an earthenware baking pan called a cazuela from Menorca, which looks like this: that was gifted to me by a friend who was visiting the island.

The form is glazed and is used by me mainly for roasting potatoes and other veggies in the oven. However, recently I have found sticky residue on the bottom of the form and on the baking tray I put it on. It seems to me that the olive oil I use seeps through the glaze and the pan and then burns/polymerizes on the bottom, leaving me with a slight mess everytime I use it. I could mitigate this a bit by using baking paper or aluminium foil, but I want to understand if my pan is broken or if I'm using it wrong.

I’ve definitely seen this. The technical term is “crazing”. Due to a mismatch in materials, when the dish is cooling after being glazed and fired, the glaze hardens and shrinks faster than the ceramic. This creates a network of tiny cracks in the glaze which liquid can seep through. It’s the marker of a crappy dish, I’m afraid. A more professionally fabricated cazuela will not do this.