The new texture system (each block and item have them and its states in their own separate image file) introduced in 13w02a brought a LOT of Z-Fighting into the game, also, it broke many textures, due to some missing files giving yourself some items crashes the game, for example, Nether Portal (ID 90) or End Portal (ID 119) have a pure white texture, redstone has weird breaking particles and if you give yourself a Monster Spawner (ID 52), the game just crashes.
Comments 4
Z-Fighting is when two textures are trying to occupy the same plane, which makes it look glitchy with each of them trying to display through each other.
Please open a new ticket for the second issue and please attach screenshots for the z-fighting issues.