Hmmm.... When it started (that image which seems to need being centered) I did exactly what you described too, i.e. center-ing it.... But I experimented - it doesn't need to. It only looks so in the preview... but once you post it - it sorts itself out! Try it!

Not too sure about the other 2 questions - steemit always does what it thinks is good for us (or itself).... and the feed thing happens every now and then, even from before - used to irritate me too; I've gotten used to it now.