This very very hard to explain, but it's so annoying, I have to give it a shot and hope someone can help.
On my laptop (only the laptop, not desktop), in Calendar, Calendar keep checking, On my Mac, Home.
This makes my new entries a BLUE color, which I don't want. I uncheck Home, yet I go in circles and the software checks that box again.
This just started happening out of the blue (no pun intended); I never had the issue before since I started using Calendar a couple of years ago.