Double spending while sending zcash

[Shawn]

Why zcashd sent more ZEC in another address?

This is normal for Bitcoin and Zcashd. Your wallet has a keypool of 100 addresses and it will choose any of those to send the change from a transaction to. See: https://en.bitcoin.it/wiki/Change Note that this only happens with t-addresses, with z-addresses it will be returned to the same address it was sent from.