String of characters appended to custom path

The team that updates the content on our most important and largest site noticed a weird behavior last week.

When assigning a custom URL path to a node, everything appears normal on the create/edit content type page. However, in the address bar when you go to the individual page/node, a string of characters is being appended to the end of the URL.

For example:
http://www.mysite.com/custom_path#.UT35URn-2kt

The string of characters is random and changes whenever you visit or refresh the page. Here are some recent strings: #.UT35URn-2kt, #.UT35Xhn-2ks, #.UT35cRn-2ks, and #.UT378xn-2kt

Fortunately, the custom url path does work; unfortunately, the link with the appended string of characters is ugly and confusing our staff that is responsible for updating site content. The only thing I can think of is that our hosting servers upgraded from PHP 5.2 to 5.3 last week, and the problem was discovered after the upgrade.

Has anyone run into this before? Is there a way to remove the appended string of characters? A setting that needs to be changed?

Drupal core 6.28
Pathauto 6.20
PHP 5.3