Power planes splits effect on differential pairs routing
It applies to any plane underneath the signal.

If you don't want or can't tolerate those effects, have your signal route over a continuous reference plane. If you absolutely have to cross the gap, and there is no way around it, you can use stitching capacitors to cross planes.



I would place two caps on either side of the signal, as close as possible to the signal trace. 

Stitching capacitors make the best of a bad situation (like getting stabbed, and having a doctor nearby). But the best, is not to cross the gap (don't get stabbed).