Aperture exports versions in random order

I'm running Aperture 3.4.1.

When I import photos from sports events (usually 500-700 per project), I rate them and then use a smart album to select the highest rated ones I want to publish.

The photos are in the smart album in sequential order (based on the filenames created by the camera).

I then select all of the photos in the smart album and choose File > Export > Versions...

My export settings are as follows:

Export Preset: JPEG - Original Size

Subfolder Format: None

Custom Subfolder Name: <blank>

Name Format: Custom Name with Counter

Custom Name: 121207-VGB (which stands for the date and name of the event)

However, once the photos have been exported to a folder, I find that they are not in the order in which they are in Aperture. For a sports event (especially basketball where the teams switch ends at the half), this makes the order of the photos quite confusing.

This is only a recent problem - Aperture did not used to behave this way, and I can't think of a setting I might have changed.

In general, I am exporting between 40-60 photos at a time.

Anyone have any ideas about why this would be happening or what I can do to stop it? The only workaround I have found is to export the photos one Aperture "row" at a time (about 13 photos). Only then do they export in the correct order. I'd rather not have to do this all the time!