Portrait pictures always export at full size regardless selected size

In iPhoto 11, I selected some pictures in an album--both landscape and portrait--and selected File -> Export. I selected "File Export" with the following options:

Kind: JPEG

JPEG Quality: High

Size: Large

File Name: Sequential

Subfolder Format: None

Text fields or checkboxes are left blank

In the exported images, all the landscape pictures are correctly downsized to 1280 x 850, while all portrait pictures are exported at full image size (2848 x 4288). The pictures are taken with a Nikon D5000. It seems like there's a bug in iPhoto in exporting portrait images at the correct size. Can someone at Apple reproduce and fix this?