Till now I always coded my interfaces this way:
I considered a retina screen as half its actual pixels, giving all interface positions the same number of pixels as it was let's say (ipad) a 1024x768 screen, but throwing in all png images as downscaled 0.5%. I mean, the button that should appear 40pixel on a 1024, needs to be a 80pixel png, so the retina will show it in all its definition. A 40pixel button will be upscaled.

Iphone 5 is behaving differently, images in there are like it was a 1136 x 640 actual screen. It was not doing this 3 months ago... ??!?!?! HELP.

Cannot publish the link right now without customer's approval...

...!
It is exactely what I needed!!
And I never ever encountered stagescale... and it was there all the time!!!!

3 months ago I was not testing things on iphone5...I thought all retinas would do the same (ipad behaves as it should).
I'm understanding this device.pixelratio right now. I will do a lot of experiments in order to make it clear to me.
THANK YOU Klaus. You saved me once again.