Disable datatable checkbox

Regarding my previous question I have another issue: is there any way to disable the datatable checkboxes in Webix?

For now, I found the blockEvent() API, but it allows me only revert the values within the onCheck event. It totally crushes the work of the masterCheckbox:

on:{
  onCheck:function(rowId, colId, value){        
    if(colId == "ch1")
      this.blockEvent(); 
    var item = this.getItem(rowId);
    item.ch1 = item.ch1?0:1; 
    this.updateItem(rowId, item);       
    this.unblockEvent();            
  }
}

Here's the snippet that demonstrates the issue.

Is there another approach? Any ideas are appreciated.