This is a "feature" of Mathematica that persists through several versions. What happens: Mathematica experiences some internal hiccup and from then on starts every Out[ ] cell with a newline, which is extremely annoying. I tried to figure out how to cancel this behavior; so far the only thing that helps is exiting and restarting Mathematica, and it helps only up to the next unexplainable hiccup... Has anybody else experienced this? If yes, has anybody found a way of canceling the unwanted leading newlines in Out[ ] cells, without exiting and restarting Mathematica?
Here is a screenshot requested by QuantumDot:

Preferences > Advanced > Notebook Options > Display Option > Magnificationto a different value? Or in that same pane, go from Printing to Working Style environment or vice versa... – Jens May 20 '16 at 16:40