According to the resolved bug
RF-11776 I've tried the attribute "columnsOrder" in ExtendedDataTable.
I have a simple test case with a data table and an action button. Within the action button method I change the String Array of the attribute columnsOrder but the columns of the data table is rendered in the old order.
I have appended a test project to reproduce it. In this test project I have an a4j ajax button and a simple button, both arent working.