On the E-M1:
- Sprocket-D custom menu, LV Close Up Mode is used to control the behavior of the focus assist magnification. Set to mode 1, touching the shutter release cancels magnification; set to mode 2, it does not. Mode 2 is the default.*
- Focus peaking is independent of magnification—there's no such automatic cancellation control, you have to turn it off manually.
* It's unclear from the description whether this works when magnification is enabled manually, or whether when you let go of the shutter release the camera returns to magnification. Experiment...
I suspect there's similar functionality in the E-M5II custom menu.
G
His question concerned adapted manual lenses, not native lenses, hence my answer. I know it doesn't work, neither with the E-m5II, nor with any previous Olympus MFT bodies I have owned (E-P1, E-P3, E-M5). You have to press the Fn button to which you have assigned the magnifier, both to start and to end the magnifying.
With manual non native lenses :
One pressure brings the target on (you can then move it on the scene and change the magnifying factor).
A second pressure and you are in the magnifying mode.
A long pressure and you get out of magnifying mode.
Two short pressures of the magnifying button in rapid sequence brings you directly in magnifying mode, skipping the first step and the last position of the target and magnifying factor will be used.
The position of the magnifying target seems to be independent of that of the regular focus target.