In more than one place, the immigration website emphasizes that medicals should NOT be completed until specifically requested. So that's straightforward enough. However, I just yesterday lodged my online application (176) and the automatic e-mail confirmation I got states the following:

If you have not already done so, please provide to the ASPC the documents listed below:
...
Form 160EH - Radiologist report on chest x-ray
Form 26EH - Medical examination for an Australian visa
Form 47P - Overseas penal clearance certificate

So does that amount to a specific request or not? Since that e-mail was an automated thing, I'd say no, but how does it really go?