Last activity time is acting like last modified time

Last activity time is acting like last modified time

When i edit the description or any field in the potential, account, contact and lead, the Last Activity Time is being updated like the Modified Time.

This is messing all workflows and reports and we are unable to track real last time of activities like mentioned in this KB article

http://crmkbase.zoho.com/what-is-the-difference-between-record-modified-time-and-record-last-activity-time