Comparators won't update it's state when a cauldron gets filled by rain

I put some comparators outside and a cauldron near each one, and when it rains and the cauldrons start to fill up, their comparators should update when that happens, but I realized that this doesn't happens.

But if I put a string floating over them, when I step over it, suddenly the comparator starts working correctly, I also checked other update types and all seem to work fine.

So this bug should be easy to fix, just when the cauldron fills up, it should seek nearby blocks in the range a comparator would be placed, and update it if it's there.

Thank you very much for your attention.