If a sprinkler is placed on a full channel and another one is placed next to it on another full channel block, both will pop off.

If a sprinkler is placed on a full channel and another one is placed next to it on a normal channel block, the sprinkler on the full channel will pop off.

If a sprinkler is placed on a normal channel and another one is placed next to it on a full channel block, both sprinklers will stay.

Oh, wait it is probably the canBlockStay() method on the sprinklers.

Yup... that's it!