I used to have a similar problem and it took me a while to work through it and get my mind around the solution (though I don't remember the details any more)
You'll probably find that you are creating those entries but they are being stored under the wrong calendar and are, therefore, not displayed. To find out, on the main calendar screen, tough the three-bar menu icon top left. This will pop up a menu display on the bottom of which is a list of calendars on the device (some of which may have been created by other apps you have loaded). Be aware that this list scrolls off the bottom of the screen - drag it upwards to see all of them. Make sure they are all checked so that you are really viewing all of the calendars and check some of the failed entries.
At the top of the event creation screen, the calendar being used for that event is shown and can be changed to the one you want to use. I can't remember how I changed the default one to the one I wanted.
Hope this helps.
