OK, this is awful!! I've got a brand new problem, obviously related to this subject. I'm guessing it happened in either a recent update of the Google Calendar app on my Samsung Phone, or a recent Android system update from Samsung.
When I create a new event in the Google Calendar app, by clicking on a day & time, it is now showing up by default as a "My Calendar" event, instead of an event in the calendar of my Gmail account. The colors are different, and if I visit the Google calendar using the browser of my Windows computer, the "My Calendar" events do not show up.
In the settings of the Google Calendar app on my phone, I can uncheck the box for "My Calendar," and those events disappear. However, when I create another event, it is still created by default as a "My Calendar" event. The other such events then reappear, and the checkbox for "My Calendar" in settings has been rechecked.
Damn, will those programmers never stop messing with things that aren't broken, and causing these kinds of problems? Has anyone solved this problem?