You're right. Q2A shouldn't ever use "start=0" since it's not necessary. It's not hugely important though - search engines can figure out they are the same page and show the right one.
Having said that, there really should be a canonical tag on the page that removes "start=0" and also rounds the start number to a real page. If you have start=20, start=40 and so on, someone can still request start=25. In this case the canonical tag should show it as start=20.
The ideal solution IMO would be normally numbered pagination - i.e. page=2, page=3.