Dynamic class name on item keeps helper classes from adding

I’m trying to add a class to an item to help color the background if a task is due soon. When I add this:

<ion-item class="item item-icon-right task-item {{task.due_date | taskDue}}" > 

It keeps the rest of the classes from being added -

<ion-item class="item item-icon-right task-item  item-complex item-left-editable item-right-editable"> 

This filter {{task.due_date | taskDue}} simple returns the string ‘due’ and then I can add a yellow bg color to that item.