Can't place tiles?

I've never had this issue with Construct before, but for some reason I can't place tiles using the Tilemap object.

The tiles show up just fine in the sidebar, and I can select them so that the cursor changes into the chosen tile. However when I click on the tile area in order to place the tile, nothing happens. The tile simply doesn't show up.

Does anyone know what's causing this?

Check the layer opacity and the tilemap opacity in the Properties Bar.

The issue isn't opacity, because otherwise I wouldn't have been able to see the cursor changing into the selected tile.