iPhone HDR - why there are two pictures (and Apple's updated user guide)

I tried using the iPhone 4 HDR feature, but I couldn't understand why I got two pictures.

I expected one image made up of the merger of two images with different exposure levels.

Apple's web site explains ...

 Apple - iPhone 4 - About the 5-megapixel camera with LED flash

... After selecting HDR, just point iPhone 4 at your subject and shoot. iPhone 4 automatically captures three photos of the scene — each with different exposure levels. Then iPhone 4 layers the shots together to create a single photo that combines the best elements of each shot and more accurately represents the wide range of light in the scene. Both the regular shot and the HDR photo appear in the Camera Roll.

I assume the first picture is the standard exposure, the high and low are discarded, and the second is the merged image.

It would be "nice" to have some more documentation. There's nothing in my iOS4 user guide about HDR. However, it turns out, the Apple website has a different iOS4 user guide. It reads on page 121:

On iPhone 4, you can turn on HDR to take HDR (high dynamic range) photos. HDR blends the best parts of three separate exposures into a single photo. For best results, iPhone and the subject should be stationary.

Turn HDR on or off: Tap the HDR button at the top of the screen. The button indicates whether HDR is on or off. (HDR is off by default.)

Note: When HDR is on, the flash is turned off. With HDR, you can save both the normal-exposure version and the HDR version of a photo in the Camera Roll, or save just the HDR version. By default, both are saved.

Choose whether to save both the normal-exposure version and the HDR version of photos: In Settings, choose Photos, then turn Keep Normal Photo on or off. If the setting is turned off, only the HDR version of a photo is saved.

If you save both versions, [HDR icon] appears in the upper-left corner of the HDR photo when you view the photos in Camera Roll (if the controls are visible).

My June 23, 2010 iO4 user guide is 18MB and 243 pages, the one I just downloaded is 19.7 MB and 258 pages. The part numbers on the last pages are different

• original: 019-1838/2010-06-22
• latest: 019-1891/2010-09

So Apple updated the manual in September. The update included a new HDR section.

I wonder if I'm the only person who's ever noticed this.