Brakes Gravity Form plugin

I’ve noticed that as soon as I specify the manual tracking number than the Gravity Forms breaks (GF).

If I leave the field “Manually enter your UA code: ” blank then GF is working.
No idea why simply specifying the tracking code manually breaks another plugin.

Any adea?
I would hugely appreciate any help.

Thanks

I could track the conflict with “Google Analytics” plugin as far as to the content filter:

line 31 file /wp-content/plugins/google-analytics-for-wordpress/frontend/class-frontend.php

add_filter( 'the_content', array( $this, 'the_content' ), 99 );

line 425 file /wp-content/plugins/google-analytics-for-wordpress/frontend/class-frontend.php

function the_content( $text ) {
   if ( !$this->do_tracking() ){
	return $text;
   }
   if ( !is_feed() ) {
	static $anchorPattern = '/<a (.*?)href=[\'\"](.*?)\/\/([^\'\"]+?)[\'\"](.*?)>(.*?)<\/a>/i';
	$text = preg_replace_callback( $anchorPattern, array( $this, 'parse_article_link' ), $text );
  }
  return $text;
}

It matches !is_feed() condition and goes off to change the mark up of links. However, the $matches array is empty following the call of preg_replace_callback(), which supposed to return unchanged $text, but instead returns empty string.

Any ideas why it returns empty string instead of un-changed string when there are no matches of links in the content?

Many thanks,
Dasha