Built-in WP gallery not showing only on a specific theme

Hi folks!

Before asking for your help, let me inform you that I’ve already tried contacting the theme author twice for his help but I’ve had no answer yet. So, I’m asking for your help, guys.
I’m internally testing Simplifi theme and I’ve realised that it does not show the gallery feature introduced in WordPress 2.5 either on home/index or on single post pages. As my actual blog theme does show it with no issues I know it is something on the theme. Please, could you give me a tip on how to solve this issue? To facilitate things I’ve activated Theme Switcher plugin on my wordpress – without links on sidebar to avoid general public spying future changes on my blog’s layout – for you to verify the things I’m saying. Here are the links, the first one is mu actual theme and the second one is the theme with gallery issues.

https://seteventos.org/index.php?wptheme=SplashMe

https://seteventos.org/index.php?wptheme=Simplifi

As my blog is not full of photo galleries I will give you a link to a post that has 3 images using the gallery feature introduced on WordPress 2.5 – please, verify it with both themes and you will see that Simplifi theme does not show the 3 images on the end of the post. The link is the one below:

sample gallery post

I know it is kind of boring and that I’m asking too much but I’ve tried to look on theme’s code and did not find where’s the problem.

Thanks a lot in advance for any help!