If you put 20 lily pads in a hopper and take a comparator output, the signal will travel for two blocks. But in case of chicken eggs, you only need six of them to get a signal of this strength.
Summary
It takes 20 lily pads to get two-block signal strength, but six eggs to get the same strength. Both items stack up to 16, shouldn't they give out signal of the same strength with the same amount of items, say, six?
This isn't a bug a comparator takes into account the number of items in a stack of that items limit, so it will be the same for other items that stack to 16. Secondly Lilly pads stack up to 64 not 16, and that's how's you could have 20 of them in a stack. Hope this helps