Great job!  :Thmbsup:
(Btw, very handy that the month is already prefilled according to which month's table you last clicked on)

That's how I like apps to work.

That's a valid argument. ;)

Moreover, using escape calls the same routine as exiting the app so everything is saved, etc.

Except for the position/size.  :P
Those are not saved when I exit the app with Esc while they are when I exit via the menu or via the upper right close button.

Nice little app!

Request: An <Edit> button in the toolbar would be nice. Now, if I made an error I have to create a duplicate and delete the previous.

Issues:
[1]
And with trying to correct an entry I found another issue:
Scenario:
1. Press the "Add Birthday" button
2. Fill in "Name", "Dec" and "10"
3. Entry is created correctly
4. Now I realize I've spelled the name incorrectly. So, I select the entry in the calendar (but there's no edit, so that selection was in vain)
5. I press the "Add Birthday" button again
6. I fill in: "Corrected name", "Dec" and "10"
7. The new entry is created. (The old one is still shown selected)
8. I press the "Delete birthday" button
   And guess which one is deleted... the last one I added <= Bug

[2]
Also, don't let the user enter non-digits ("abc") or invalid numbers ("300") in the day spinner text box.

My 2 cent...

btw, where does CFD in CFDButton stand for?  :tellme: