This bug isn't necessarily important, and is very low-priority because the z-fighting is not shown unless the block covering it is broken, which is impossible in survival.

The z-fighting is shown when the bedrock + end crystal base block is viewed from underneath in the end pillars, the end pillar has no collision therefore fighting occurs. The fighting also happens if the bedrock is replaced with any block from underneath in the pillar, the crystal will just detonate if the bedrock underneath it is broken from above.