If a table contains an invisible column (which is new a new feature in 12c) this column is included in the export/generated sql as invisible, which works as expected.
In dialog "edit table" it not possible to edit this column because it is not included in the column list.
If would be useful if there is a checkbox to enable/disable the visiblitity of "invisible columns" in the column list of the "edit table" dialog.
If the "invisible column" is not shown in the editor, it is for example not possible to make it visible.
The same would be fine in the data grid too, otherwise it is not possible to fill some data into an invisible column.