String-along, is this possible and is it an attack?
A miner can always lose out if someone else mines a block at approximately the same time as he does. A miner will always continue building on his own block if he finds one before he processes a block found by someone else. It is never to a miner's advantage to ignore a block found by someone else unless he himself has found a block at almost exactly the same time.

So this is all behavior as expected.

When you mine a block, everyone else who has not found a block has a strong incentive to mine after your block. If they don't, they have to find two blocks to get any credit at all. If they find one block first, the rest of the network will ignore it.

If you control 51%, you effectively control 100%. That is also expected behavior.