The resolution of this issue depends on whether the color texture uses pre-multiplied alpha or not. Unfortunately, there is no way to tag or generate textures for different alpha compositing modes in Unity right now. There are no guidelines for proper texture authoring, either. Therefore, we cannot make any assumptions about the makeup of the color texture, which makes the bug impossible to fix.
In general, I would suggest using pre-multiplied alpha for alpha blending, and avoiding it for alpha clipping.