The code has a built in contingency that checks if the value drops below zero, to set it to zero. If that doesn't happen, obviously it's a compatibility issue, or zero has stopped equalling zero, which implies the universe has ended. Obviously the second case being unlikely, I think you aught to make sure nothing silly is enabled.
It is also equally possible that blockland itself is to blame, deciding against performing variable changes for whatever reason. Although this isn't likely either.
If you can replicate the circumstances of this occuring, and give me a definitive reason why it's happening, I can fix it. Because I have never recieved this issue during testing.