In v2.5, Using [File-->Export-->Export file(s)] does not persist the columns selected for export. If users routinely need to export a specific set of columns, this can become very tedious as every single time the user will need to select their columns from the list.
A workaround is to add a Table View to a tab that only contains the columns you want to persist. Selecting [ViewTools-->Export view data] will present you with an Export dialog that has preselect only the columns defined in the Table View. It even persists the order of those columns.
Thanks for the suggestion. We'll consider making the columns persist in future. However your workaround is a good solution - you might want to create a new tab specifically for this, so you don't pollute the views of your working tabs.
I like to do exactly this, usually on an "Export" tab, even going as far as to have several different tables on this "Export" tab - each with different columns visible, and different levels of aggregation (if needed); then I use the View Header to remind myself what the export is e.g. "export: FullData.XLS" or "export: TopClients.XLSX" etc.