Forgive me if i'm wrong; but Antpool appears to be doing the same thing (found block, not submitting straight away, mining on header of found block, submitting both in quick succession).. standard behaviour from them?
This is not quite correct. They are submitting it straight away as they have a lot to lose by not submitting it. It's just that they start mining on the header of a
any pool's found block
without verifying it's valid. As they're only mining on the header they are also unable to generate work with further transactions in it so they are always empty transaction blocks they're mining. In their next work update from the pool they are then working on verified blocks with transactions mined in. The effect you are seeing is that SPV mined blocks by design only ever occur within a short timespace of a previously solved block. The fact that it's often two blocks back to back by the same pool is purely because those pools are TOO FUCKING BIG and get lots of blocks.
in this case, where they know the previous block is valid b/c they mined it, why wouldn't they simply mine the next with tx's in it? the reason these spv miners do what they do is b/c they don't want to waste time validating
another pools just received block, which is not the case in this situation since it's their own.