Missing calendar on ipad 2

I use several Google calendars to sync with work, family and for personal use of course. I check the calendars on my computer, phone and Ipad 2. Today I noticed that one of my calendars was not appearing on the Ipad, but visible on the computer and Nexus S. Why?

After some googling i found the solution here and the reason is that one of calendars was not checked on my Google account's synchronization settings page (https://www.google.com/calendar/iphoneselect?pli=1). Why was a checking missing for one of my calendars? I have no idea.

 

Edit: I managed to reproduce this problem

1. create a new calendar on calendar.google.com
2. open calendar app on Ipad, the new calendar is missing
3. go to https://www.google.com/calendar/iphoneselect?pli=1, the new calendar is unchecked

So, new calendars are not synched to Ipad!
(My account type for calendar sync are set to Gmail on the ipad.)