Beacon beam renders slightly differently inside of a boat

The bug

When a beacon beam travels through a boat, any part of the beam inside of the boat appears very slightly lighter than normal.

How to reproduce

1. Place and activate a beacon
2. Place a boat such that the beacon beam will pass through it

Expected results

The beam would look pretty much constant as it passes through the boat.

Actual results

The area inside of the boat looks very, very slightly lighter.