The bract and flower layers of sunflower heads are displaced when at distances of over several thousand meters from the spawn point. Shown is the two fused layers z-fighting (z and x -500,000), as well as their awkwardly bent shape when viewed from the side.
Tested using the 'infinite' and 'flat' world types.

Edit:
Added updated information. It appears that the issue's first occurrence is much nearer to the spawn then I previously estimated. Flying directly outward on a positive z-axis in creative mode for 2 hours and 10 minutes, or approximately 80,000 meters, resulted in a slight displacement of the flower layer. Attached a screenshot of this, showing a sunflower in a superflat world.