Ember ember-views.render-double-modify

Using Ember.2.1.0-beta4

I am getting the "ember-views.render-double-modify" in a function triggered by the "didReceiveAttrs" of a subcomponent.

I tracked down the statement this.set('_columns', columns) that triggers the error. However, AFAIK this is the first time the attribute is modified.

To debug it, I created an observer for the modified attribute, and put a breakpoint there. However, the observer is only called once and the error is still there, so it looks like this is the first call.

How should I debug this -- is this an Ember bug, or are there other restrictions on setting attributes that aren't clear in the error? Note that the attribute is used in the component's template. Also the attribute is used in other computed attributes (e.g. _columns.@each.width and _columns.[]).