When I edited a question, this is how it appear :
Why am I over the OP's and not next to ?
Recently the site-design changed.
A main reason for this was to make the site "responsive." This means, at least in my naive understanding, that it will try to adapt as good as it can to the size of the display or window available.
Thus it starts to put things at different places. If you look in a larger window or zoom out this should go away.
This is for all I can tell by design. I can reproduce it here. I make the window small it is as you say, I maximize it is as always.
On a small display it likely will always be as you say. On still smaller ones the "sidebars" stop being sidebars and show up at the end. And so on.
If you do not like it, you can give your feedback on the thread mentioned above, but it's not a bug in a proper sense.