REDUNDANT MECHANISMS that fail to communicate with one another can make using Mac OS X Lion more confusing than it should be.

Consider the screenshot shown here. While Apple’s Software Update knows that I have downloaded the latest version of iPhoto (“Your software is up to date”), Apple’s App Store, pulling from a different database, does not know that I have already installed iPhoto. It only knows that a new version is available.

Because the App Store’s left hand doesn’t know what Software Update’s right hand has already downloaded and installed, the App Store flashes a red download alert badge, urging me to download 500MB of Apple software that Apple’s OS has already installed on my Apple machine.

Suppose I don’t bother to check Software Update and verify that the App Store’s “Update” tab is urging me to take a nonsensical action. Suppose I actually go ahead and click “UPDATE” in the App Store’s “Update” tab. What will happen?

The software, all 500 MB of it, will download again, and install itself again. That’s what will happen.

And the cream of the jest? After installing the software again, if I click into the “Purchases” tab of the App Store, the “Purchases” tab will inform me that an iPhoto update is available, and urge me to install it. And if I have been huffing nitrous all day and take Apple’s advice, the 500 MB package will download for a third time and install itself a third time.

And you thought Retina images were tough on bandwidth.

(A friend tells me that Mountain Lion resolves this clustercuss by removing Software Update from the equation. I suspect that those of us still using Lion are receiving unintended anal leakage from UI decisions that make sense in Mountain Lion but are idiotic in Lion. Click