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.
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.