Submitted by cmichel, also found by 0xsanson, broccoli, and pauliax
The ConcentratedLiquidityPool.burn function sends out amount0/amount1 tokens but only updates the reserves by decreasing it by the fees of these amounts.
This leads to the pool having wrong reserves after any burn action.
The pools balance will be much lower than the reserve variables.
As the pools actual balance will be much lower than the reserve variables, minting and swaping will not work correctly either.
This is because of the amount0Actual + reserve0 <= _balance(token0) check in mint using a much higher reserve0 amount than the actual balance (already including the transferred assets from the user). An LP provider will have to make up for the missing reserve decrease from burn and pay more tokens.
The same holds true for swap which performs the same check in _updateReserves.
The pool essentially becomes unusable after a burn as LPs / traders need to pay more tokens.
The reserve should be decreased by what is transferred out. In burns case this is amount0 / amount1.
sarangparikh22 (Sushi) confirmed
