There are 3 options for the leaves setting in minecraft: fast, default, fancy.

Problem:
If this setting is set to "fast", this results in leaves being transparent at short distance and "fast" (visually opaque) at long distance. This sometimes creates visually unpleasant views, especially when moving.

Solution:
Either make it so the shader listens to whatever option is set in game settings or add setting to configure this in the shader itself. That will help maintain consistent look and save some fps for people, who want to use "fast" leaves.