Steps to reproduce:

❯ bitcoin-cli --rpcuser=x --rpcpassword=y -regtest getnewaddress "" "bech32"
bcrt1q6rhpng9evdsfnn833a4f4vej0asu6dk5srld6x

By BIP173 Segwit address format bitcoind should return a tb prefixed address for testnet, and by developer examples, regtest is a blockchain with the same basic rules as testnet.

Expected behavior

bitcoind should return a bech32 address with the same prefix as testnet.

Bitcoind version

0.16.0rc1