It's a feature, not a bug If you press the camera button fully in one go, the camera assumes you want a picture as fast as possible, and it skips focus. Can be quite useful actually. I think it uses a preset of about 1 meter, but I could be wrong.

In my experience it is not necessary to use the macro mode for taking pictures of an A4/Letter size document, or even a part of it. It is much more important not to move the device.

Also, if you want manual focus, install Ifocus. (Quite unique for a phone!). For taking real close-up macro shots it beats the macro mode.