When exporting from a view in 2.8 web start with 'allow export' turned on, you are unable to select a 'save as type' so the only way you can do it is from 'File' -> 'Export'
Alex - is this about Web Start deployment? If so, the Omniscope displaying the file is a free Viewer, which can only export csv from the sandbox...and can do that only if the IOK file is an 'empowered' IOK file owned/saved/published by a ServerPlus license. Is this the scenario you are asking about?