Why can’t I subscribe to my own magazine on the Google Play Store?

A developer cannot purchase anything from his own developer account.

This is not a bug but just the way the Google Play Developer Console has been set up.

To fully test your app, you will need to create a test account in the Developer Console and then install your app on a device where that is the primary account.

Please see http://developer.android.com/google/play/billing/billing_testing.html