The Bug:

Some tree leaves from certain types stop pale oak saplings from growing up.

Steps to Reproduce:

1. Create a flat world
2. Place a 2x2 square of pale oak saplings
3. Place dark oak leaves on top of the pale oak saplings.
4. Notice the pale oak sapling will not grow even with bone meal.

Expected Results:

All tree leaves would allow pale oak saplings to grow up.

Observed Result:

Certain tree leaves stop pale oak saplings from growing up. Here is a table.