Weird problem when uploading image, auto set center alignment

Hi i got a weird problem, when I upload a image in WP, it will auto set center alignment for me as shown in the picture below

https://img8.imageshack.us/img8/9408/thegabajingabloggpgtblo.gif

And when I insert to post, it appear centered, but once I published and view the my blog, it is show as left alignment, I will then need to edit my post, reset the image alignment and set it center via the paragraph center button.

it’s weird. I not sure is it my theme css or the WP core css fault.

Here’s my theme css https://www.siegebox.net/blog/wordpress/wp-content/themes/dailydiary/style.css

or maybe it could be one of my plugin that I use, “TINYMCE Advance”?

How do I not having it auto select the CENTER alignment checkbox for me?