Why I can use a lower gasPrice than the node I set in --gasPrice

Question

I established a private network recently and I use web3.eth.sendTransaction({from:"0x14ca04ff85747def87d6c6c566db84cc24e4643b",to:"0xa04fce8906c870a47a8a7f5f7547dfc4a62cae7a",value:"1000000000",gasprice:"0x0"}) to force the gasprice is 0eth.

I supposed this transaction will be failed cause the ONLY node I start use the --gasprice 1000. But it succeeds and with NO extra charge in gas.

Thanks~