Actually for being exact, if the first page returned in search result (becoming the $post global) contain a timeline shortcode (WPVT).
The shortcode is actually displayed when shortcode processing is done by process (before theme display).
It results in a timleline outputed above the doctype that break the whole page.
The bug is in the term "outputed". It's not returned as given in ex. in wp doc there : https://codex.wordpress.org/Function_Reference/add_shortcode
So i suggest you replace the "echo" call in wp-writeco-timeline.php by a "return" :-)