Not a good idea, especially through an intersection. Think about when you wait in the left turn lane in your car, and a bus comes the other way, going straight. What side of the bus do you see? The left (driver) side. If someone is on a bike behind the bus, towards the left side of the lane, you can easily see him/her from your car. If the cyclist is behind the rear right corner of the bus, you won't know the cyclist is there until much later, possibly even not until after you have started your left turn across oncoming traffic lanes.

Yes, a bicyclist tucked up behind a bus in the right rear corner can't be seen. OTOH- he can't be hit by a left turning vehicle unless it has warp drive. Even if the driver tries by timing his turn to just clear the corner, and taking it in as tight a radius as possible, he can't come to within 5-10 feet of the right rear corner. Since the bus and bike are both also moving, that means they'll have left that position anyway.

However, it's important to stay tucked into the protective corner, and not hang back far enough where you might be hit.