The sidebar always hides when we open the dmg files and using CMD+OPT+S or CMD+OPT+T also does not work always. I know apple has screwed up this and there is no reason to hide the sidebar when you open the dmg files. Is there any option to keep the sidebar permanently visible?
This is a big issue puzzling a lot of people. It is on my TODO list to resolve it somehow. But it is a hard task, because Finder internals related to different modes of operation and display styles are quite complex.