I played around with this showcase example:

1. I created a custom field with the formular editor in this example
2. The new column appeard
3. I saved my settings
4. I swiched back to the default view
5. My custom column did not disapear

I guess this is a bug... right? Seems that customn columns do not get removed in fieldState and ViewState. The "Default" view did not contain this column so it sould disapear and when I choose my saved view... it should appear again.