This is what I found on a firmware update that seems to address the problem. However, firmware version is at Ver. 211 already. As stated above this occurrence only happens using the EVF and at apertures between f2.0 and 3.6. It does not happen using the OVF or LCD.
The firmware update Ver.2.11 from Ver.2.10 incorporates the following issue:
The phenomenon is fixed that when pressing the shutter button halfway under certain conditions, the live view can flicker.