As segwit is active on testnet, blocks will only be downloaded from NODE_WITNESS peers. Though, exactly those peers are disconnected after `BLOCK_STALLING_TIMEOUT = 2` seconds. I am running master (6e6ab2c)

This behavior is consistent across restarts. Sample [debug.log](http://pastebin.ubuntu.com/23058327/) and [getchaintips](http://pastebin.ubuntu.com/23058325/).

It is possible that I shot my own foot at some point, but it seemed smelly enough to create an issue.

{
    if (*pindexPrev->phashBlock == chainparams.GetConsensus().hashGenesisBlock)
        return true;
    int nHeight = pindexPrev->nHeight+1;
    
    CBlockIndex* pcheckpoint = Checkpoints::GetLastCheckpoint(chainparams.Checkpoints());
    if (pcheckpoint && nHeight < pcheckpoint->nHeight)
        return state.DoS(100, error("%s: forked chain older than last checkpoint (height %d)", __func__, nHeight));
    return true;
}
bool IsWitnessEnabled(const CBlockIndex* pindexPrev, const Consensus::Params& params)