Seems that Android's Google Calendar allow modification only if your account email is equal to the one written into the event's organizer field.
Steps to reproduce
- Go To Settings > WebTop > Personal info and change the email address to something different to your full username
- Create a simple event under a calendar with active EAS sync
- Open your Android Google Calendar app and then try to edit the event
- Event can be edited
- Event is displayed with a white background and cannot be edited