if some process locks a block in round 0, then 0 is valid proposal.POLRound in rounds > 0

This condition is really hard to get. Initially, lockedRound and
validRound are set to -1 as we start with round 0.

Refs #2702

consensus/state.go

@@ -1425,9 +1425,9 @@ func (cs *ConsensusState) defaultSetProposal(proposal *types.Proposal) error {
 		return nil
 	}
 
-	// Verify POLRound, which must be -1 or between 0 and proposal.Round exclusive.
-	if proposal.POLRound != -1 &&
-		(proposal.POLRound < 0 || proposal.Round <= proposal.POLRound) {
+	// Verify POLRound, which must be -1 or between 0 inclusive and proposal.Round exclusive.
+	if proposal.POLRound < -1 ||
+		(proposal.POLRound >= 0 && proposal.POLRound >= proposal.Round) {
 		return ErrInvalidProposalPOLRound
 	}
 

types/vote_set.go

@@ -158,7 +158,7 @@ func (voteSet *VoteSet) addVote(vote *Vote) (added bool, err error) {
 	if (vote.Height != voteSet.height) ||
 		(vote.Round != voteSet.round) ||
 		(vote.Type != voteSet.type_) {
-		return false, errors.Wrapf(ErrVoteUnexpectedStep, "Got %d/%d/%d, expected %d/%d/%d",
+		return false, errors.Wrapf(ErrVoteUnexpectedStep, "Expected %d/%d/%d, but got %d/%d/%d",
 			voteSet.height, voteSet.round, voteSet.type_,
 			vote.Height, vote.Round, vote.Type)
 	}