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.

State(pfrom->GetId())->fPreferHeaders = true;
    }
    else if (strCommand == NetMsgType::SENDCMPCT)
    {
        bool fAnnounceUsingCMPCTBLOCK = false;
        uint64_t nCMPCTBLOCKVersion = 1;
        vRecv >> fAnnounceUsingCMPCTBLOCK >> nCMPCTBLOCKVersion;
        if (nCMPCTBLOCKVersion == 1) {
            LOCK(cs_main);
            State(pfrom->GetId())->fProvidesHeaderAndIDs = true;
            State(pfrom->GetId())->fPreferHeaderAndIDs = fAnnounceUsingCMPCTBLOCK;
        }
    }
    else if (strCommand == NetMsgType::INV)
    {
        vector<CInv> vInv;
        vRecv >> vInv;
        if (vInv.size() > MAX_INV_SZ)
        {
            LOCK(cs_main);
            Misbehaving(pfrom->GetId(), 20);
            return error("message inv size() = %u", vInv.size());
        }
        bool fBlocksOnly = !fRelayTxes;
        
        if (pfrom->fWhitelisted && GetBoolArg("-whitelistrelay", DEFAULT_WHITELISTRELAY))
            fBlocksOnly = false;
        LOCK(cs_main);
        uint32_t nFetchFlags = GetFetchFlags(pfrom, chainActive.Tip(), chainparams.GetConsensus());
        std::vector<CInv> vToFetch;