Dear Takayuki Miyoshi,
If it's not not a bug, what is it? Unsupported feature? No disrespect. You plugin is GREAT! But this was a bummer, just before I had to deliver my work to a customer. Very disappointing, but still very grateful for your plugin. So, don't get me wrong. HTML5 & CSS3 still have a long way to go to be supported be all major browsers.
I had to go back to your previous version of the CF7 with additional datepiker plugin. Otherwise, no delivery - no money. You know that.
Anyhow, thank you for you reply! Keep it up, I support CF7!