Redstone torch not matching signal

In some cases (see attached world file) the redstone torch does not properly match the signal to the block.

As example, see the world file. This is like an item "sorter". The middle hopper is filled with redstone and sandstone in such a way that adding one more redstone causes a signal (disabling a redstone torch) and drops an item into the hopper underneath.
It mostly works. However, if you put 15 redstone (as added to the inventory in the world file) in the top hopper, the torch will start blinking and suddenly turn off. It will turn off for too long, even after the signal on top of the block with the redstone torch is off.
To clarify the bug, see the redstone repeater and the redstone torch. They both have as source the same block, so the redstone torch should be turned off exactly when the redstone repeater turns on. This is not the case, however: the redstone repeater works as expected, but the redstone torch suddenly turns off and doesn't get updated.
This worked fine before update 1.8.