Missing resource warning when loading up the game

Upon launching snapshot 4, the launcher declares this in the log:

17:16:02.659
Missing resource minecraft:textures/misc/forcefield.png referenced from minecraft:textures/misc/forcefield.png

17:16:02.662
Missing resource minecraft:textures/environment/rain.png referenced from minecraft:textures/environment/rain.png

17:16:02.663
Missing resource minecraft:textures/environment/snow.png referenced from minecraft:textures/environment/snow.png