On Sat, Jul 11, 2015 at 10:24 AM, Jorge Timón <jtimon@jtimon.cc> wrote:

I think it would be more rational for them to keep mining on top of the old block until they've fully validated the new block (which shouldn't take so long anyway), even if this slightly increases the orphan rate.

Increased orphan rate means that the network is (slightly) less secure.

If miners have a 5% orphan rate, then an attacker can launch a 51% attack with 49% of the network.

It isn't a massive difference, but it is there.

As long as miners switch back to non-SPV mining after a timeout, SPV-mining is safe for everyone.

The average cost to the miner from building on an invalid block is small, as long as invalid blocks only happen rarely.

Miners still have an incentive to do full validation, so that they can include transactions and get transaction fees.

SPV-mining is to prevent hashing hardware from having to waste power when it isn't needed.

It may be less of a problem if (when?) electricity costs dominate hardware capital costs.