After receiving all these notifications about the "new" Zoho calendar I decided to check it out and try working with it. 

I would like to use the calendar for my GTD-like system/workflow, so I imported the iCal URL of my Trello GTD calendar.

I de-activated (unchecked) all my other calendars, in order to have a clean view of just my GTD tasks and such, but despite I turned all other calendars off, events/dates/holidays/etc. still show in this new GTD calendar.

What am I missing?