imessage sending and receiving text on same phone

Hi all,

I have 2 iphone 5's under my Apple account. One is mine (Joon) and the other is my wife's (Esther).

Today, I noticed a weird behavior. When I send a text message (imessage) to my wife, I automatically receive the same exact message sent from myself. Basically, Esther texts me "hello", I reply back with "hello". Normally, I should not receive anything on my phone when I send out a text. But then I receive a new message sent by Joon saying "hello". It's pretty annoying.

How do I tweak this? Just FYI, my phone is the main phone and my wife's is my secondary phone. Also, my wife's phone does not behave like this.

Thanks!