Comparator is miscounting Hopper's contents

Put the summary of the bug you're having here

What I expected to happen was...:
in the Hopper:
22 items of 64 (Stack-able) have a one block strength
5 boats have a 15 blocks AND 4 blocks are 12

4 boats and 21 planks should have been 13 blocks

What actually happened was...:
4 boats and 22 planks have only a 5 block strength

Steps to Reproduce:
1. put 5 non stack-able in a Hopper
2. remove the 1st(or any)
3. replace by 22 item of a stack-able item of 64