OS X QFileDialog::getSaveFileName doesn't allow selection of file with extensions like .tar.gz

When using QFileDialog::getSaveFileName with a filter looking like:

"Archives (*.tar.gz *.zip")"

The native dialog doesn't allow to select the tar.gz files. AFAIK it's a limitation of NSSavePanel that doesn't support double extensions.

Should we workaround that and build the list using only the last extension so in this case "gz" and "zip" and document the behavior ?
Or just update the documentation and explain the limitation on OS X ?