Olympus disabled the 4.2 firmware update on the E-M1. This is their official press text:
The award-winning Olympus OM-D series has received excellent reviews from a wide range of users. With stunning, compact designs packed with revolutionary technologies, the OM-D series provides incredible speed, outstanding image resolution and a host of shooting features to meet the needs of the professional and enthusiast photographer, alike.
There have been a small number of reported issues with the latest E-M1 firmware version 4.2. As a result, Olympus has proactively suspended this firmware update in an effort to evaluate the reports.
Olympus has been able to confirm that it is a unique group of settings that cause the issue. The camera does not perform properly under the following conditions:
Using HDR, Focus stacking, Hand-held starlight in scene mode, and keystone compensation with Rec view ‘Off’.
When Rec view is turned on, the problem does not happen. Affected users are advised to turn Rec View on to avoid issues.
For those E-M1 owners who have not yet updated their Olympus firmware to version 4.2, and whose current firmware version is version 4.1, no action is necessary.