This is occurring on Handheld Contact version 1.0.6.0 for Android devices.

If you make a change to an existing activity (Example: change the duration of a task from 10 minutes to 1 hour), the Handheld Contact application is not refreshing.  This is also an issue when deleting the activity.  After it is deleted, Handheld Contact will still show the task until the refresh takes place.

To correct this issue, you simply need to 'refresh' the calendar.  The easiest way to do this is to skip ahead one day (or month) and then go back to the original date.  A 'Loading...Please Wait' screen will quickly flash up between switches.  Once you go back you will see the activity changed to 1 hour or you will see that it was removed from the list.