Warning: Unknown block versions being mined! It's possible unknown rules are in effect Recently, my full node (Bitcoin Core 0.14.2) displays this for both HD and non-HD wallets:


  Warning: Unknown block versions being mined! It's possible unknown rules are in effect


What does this mean?
Miners have started signalling for BIP 91, which sets bit 4 in version numbers. When BIP 91 activates, it will force miners to set bit 1 (which then indirectly will cause activation of BIP 141 SegWit).

No software release has implemented BIP 91, as a result, it warns because it sees an unknown feature rollout with significant support from miners.