Well. Lets assume a there's a map in an item frame. And the chunks where the map is showing are loaded. Then in those chunks you set an area of air blocks into stone on the surface. The newly placed blocks aren't updated on the map.
Note: You don't have the map in your inventory, it's just on in the frame. both the chunks of the map and the item frame's chunks are loaded.
I've noticed that the map updates when the player has it in his hand. I've tried to make a workarount by giving him this specific map in his hand, and removing it in the same tick but it doesn't seem to solve the problem. I'm not sure if it's a bug or a feature, but it would really come in handy if the map would reload its self by its self without the player having it in his hand.
This is an intended feature. It's actually quite useful, because it means you can have before/after map displays.
To update the map, just pick it up and hold it for a moment.