Hello Damir,
I am really sorry for the delay of this reply. After countless hours of debugging and testing, this issue is a very nasty bug and it requires a lot of refactoring to get this fixed altogether.
I have applied a quick patch for you so that we are able to retrieve first image from the blog post (legacy) behavior. However, to really fix this, we need to re-think the way we are retrieving all these media from the post content. It is very very tricky.
In case you need to upgrade in the future, the changes I made is in /administrator/components/com_easyblog/includes/post/post.php by adding the lines below at line 352:
[gist]
$this->original_intro = $post->intro;
$this->original_content = $post->content;
[/gist]
Then, at line 3957, I have also added the codes below,
[gist]
$content = $this->original_intro . $this->original_content;
[/gist]
This is just a monkey patch which I am not happy to include in the core of EasyBlog. We need to really re-think and fix all these issues once and for all.