Cannot Connect to App Store from managed account?

This is an odd one...

Context: My son has a MacBook Air. My account is the "admin" account, his is a managed account. His account is permitted to run the App Store.

Note that the App Store is configured under his Apple ID under both his login and mine. I want the software purchased to get registered to him so that he has access to it on future machines.

On Lion: When the App Store application is started from his (managed) account, it asks for an administrator password. Once this is given, it connects to the App Store without difficulty, and is willing to perform updates.

On Mountain Lion: the App Store application runs fine from my (administrator account). When it is run from his (managed) account, it asks for an administrator password, but then fails to connect to the app store. This is true even though his (managed) account has permission to run the App Store application.

Anybody have any clue what is happening? I can run the App Store application from my account if need be, so this isn't critical, but it's the kind of behavior change that makes me very nervous; the App Store application is a pretty critical subsystem.

Thanks!