This is on 1.8.5.0 for Windows. Whenever I start up Scrivener, the “*” change marker next to the project file name on the window header is there. (If I make any change, it disappears after a couple of seconds, just as it should.)
There are some things that change on the disk when you load a project. The search index may be updated if certain conditions warrant doing so, a lock file will be added (this is how other instances of Scrivener can detect when a project looks to be opened already), and maybe a few other things happen as well.