When we added ExcelExportAction (in form of jmix-ui-export library) to tables in our project, and started using it to export data, whe have noticed that it handles big decimal fields with NumberFormat annotation quite strange. It creates text cell with formatted value of actual number instead of numeric cell with number itself and provided format. So if upon getting excel sheet somebody decides that he needs to do things like calculating column total ore use other aggregation, he needs first manually turn cells into numeric ones they should be.
As far as debug shows, it is fault of AbstractTableExporter.getColumnValue that automatically formats number before cell type is defined in ExcelExporter.formatValueCell