If I enter a value into the date component and then delete the value (as in click into the component and use the del key or select the text and hit del) when I click out of the component, the old value pops back in. It's like a zombie - you can't kill it!
However, if I enable the Clear button and click it, that is the head shot that finally kills the zombie, I mean date value.
Got zombies on the brain I guess 
Anywho, you should be able to delete it from the keyboard as well.
