I’ve only noticed this on the Windows version of Scrivener, though I load some of the same projects on both Windows and Mac versions. Often times, I will load a project, click on a document in the binder, and all or most of the text will be selected (as in ready to be copied or deleted). I click into the editor to remove the selection, but it’s the same thing throughout my project. I’d very much like Scrivener to stop doing this, and can’t think of a single reason why I would want to preserve a selection in a document that isn’t loaded in my editor.
In case it’s relevant, I synchronize my projects on Dropbox, and open them directly from one of its sub-folders on both Windows and Mac.