When the page first loads, the task form isn't displayed properly (this is reported in a separate bug). In addition to that, any Task Action taken when the task form is in this state (e.g. the first task action to be taken after navigating to the task details page) will result in two growls: 1) Task has been updated 2) Task <action> has been completed
Verified in S-RAMP 6.0.0.ER1