If you throw a stack of items into a hopper that can't take in all the items from the stack (because the hopper is full), it will correctly take in as much items as it can, but connected comparators won't update.

Reproduction steps:

• place a hopper, a comparator and 15 redstone for visualization
• fill 4 slots of the hopper inventory with full stacks of dirt
• fill the 5th slot in the hopper inventory with half a stack of dirt
• throw a full stack of dirt into the hopper

Observations after completing the steps above:

• the hopper will take in half of the stack of dirt that was thrown at it and the other half will bounce off (expected behavior)
• the restone signal originating from the comparator won't update although the hopper is now completely full (bug)
• a block update adjacent to the comparator will update the redstone signal to its proper strength
• the item stacks in the hopper don't have to be all of the same type
• the bug also occurs for example if 2 slots contain a 60 dirt stack (the other slots are full) and you throw a stack of at least 9 dirt in the hopper

Pseudo code that illustrates the conditions that have to be met for this bug to occur:

(space for items of type A in the hopper) < (stackSize of type A items thrown in the hopper)