caution money is for protection of the lessor (property owner) from non-payment of rent or damage of property / furniture.
e.g., if you have not paid the rent for a month, the lessor can deduct the money from the caution money he is holding, so as to cover his loss.
However, if you decide to terminate the contract within 1 yr (fixed term), you have, strictly speaking, to pay for the remaining rent for that year. This is irrespective to your caution money. The lessor can still deduct your caution money, on top of that, if you damage the furniture.
Of course, there is always another way to deal with it. You can negotiate with the lessor to pay less, coz the lessor can lease the flat out again. He may get the same, or even higher rental income if the property market booms. As a result, you can chat with the lessor to ask for just pay for his damage (i.e. additional commission for agent in pro rata basis, and loss of rental income if it drops in the succeeding lease contract)