Hi!
I’ve found the problem. By default the search tries to execute the shortcodes found in the content and run the though the “the_content” filter. That command was stuck for some reason. I’m guessing that a plugin or maybe the theme has another filter attached to the “the_content” hook and that made an infinite loop.
The solution was rather simple. I turned off the “Run shortcodes found in post content” and enabled the “Strip shortcodes from post content” option instead on the advanced options panel: http://i.imgur.com/r2Zrn8g.png
The search should work now on full speed 😉
Thank you for the proper details, it made my work much faster.