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.

bool fNotify = false;
    bool fInitialBlockDownload = false;
    static CBlockIndex* pindexHeaderOld = NULL;
    CBlockIndex* pindexHeader = NULL;
    {
        LOCK(cs_main);
        if (!setBlockIndexCandidates.empty()) {
            pindexHeader = *setBlockIndexCandidates.rbegin();
        }
        if (pindexHeader != pindexHeaderOld) {
            fNotify = true;
            fInitialBlockDownload = IsInitialBlockDownload();
            pindexHeaderOld = pindexHeader;
        }
    }
    
    if (fNotify) {
        uiInterface.NotifyHeaderTip(fInitialBlockDownload, pindexHeader);
    }
}
/**
 * Make the best chain active, in multiple steps. The result is either failure
 * or an activated best chain. pblock is either NULL or a pointer to a block
 * that is already loaded (to avoid loading it again from disk).
 */
bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams, const CBlock *pblock) {