Don't worry about it. I can't say why there is measureable low impedance between the rails... I haven't given it any thought.
But I wouldn't worry about it. Power it up. I'm sure it will be fine. If you are really worried, or if you are into proper first time power-up procedures, you'll bring your design up slowly using a variac or variable DC power supply. That way you can monitor the supply current and voltages. It will be obvious if you have a problem.