Behaviours set Description added multiple times

Assign the following behaviour to the priority field 

void setEnvironmentWhenHighPri() {
    FormField formField = getFieldById(PRIORITY)
    FormField descField = getFieldById(DESCRIPTION)

    if (formField.getValue() == "1") {
        descField.setDescription("<div class=\"warningBox\">Please explain why priority is Blocker.</div>")
    }
    else {
        envField.setDescription("")
    }
}

And change the value of the priority to highest. You will see a

<div class=\"warningBox\">

Under the description filed but

• not in the right position 

Then change the value of the priority field to something else

• The description message is still there

Change the priority value to Highest again

• It will create another one div 

There is already a failing test for this 

com/onresolve/jira/groovy/functional/behaviours/TestBehaviours#testSetDescription()