This is one that I spotted while watching Minecrafters on Youtube - when crouching, the player's name tag will cause effects like the Nether Portal, water, and some others to become invisible. I don't have a comprehensive list, and the issue is only really present on multiplayer servers.
Environment
Put your operating system (Windows 7, Windows XP, OSX) and Java version if you know it here
Linked issues
Comments 2
This ticket is actually a duplicate of MC-162693.
Please include a screenshot of this