Flashing

The presence of glossy patches on a painted surface is known as flashing

This can happen when a drywall patch wasn't primed using a texture process to match the rest of the wall.  To help avoid flashing...

• When spot priming over patches (previously painted walls), use a 10 mill nap roller and feather out the edges.
• Always use a quality primer over freshly applied or textured drywall. Using cheap primer (or paint) won't cover properly and will always give you some flashing.
• Always sand walls corner to corner after priming.
• When doing long hallways with light shining down the wall... we always spot prime a second time with Benjamin Moore Aura as this brand is without question the best paint on the market.