I have created a pivot from my power BI dataset (using Get data / powerBI dataset - I have a channel preview account )
In a traditional pivot you can expand and collapse data in columns from the header regardless of whether you have already expanded some individual items int he column.
In the powerBi dataset based pivot , if you have already manually expanded one or two items (in say columns 3 and 4) you have to go back and collapse everything from the first column and then re-expand whole columns to show all the data. If you collapse the entire field for column 3 (currently part expanded) and then expand all on column 3 it will just go back to your part expansion - not to expand all. Until you collapse all in all the previous columns.
Community support over in Power BI think it is designed but would be interested to here from the excel experts - is this expected behaviour?