<p>Let's say that there is a solution that contains two projects (Project1 and Project2).</p>

<p>Project1 is set as a StartUp Project (its name is displayed in a bold font). I double-click some file in Project2 to open it. The file opens, but something else happens too - Project2 gets set as a StartUp Project.</p>

<p>I tried to find an option in configuration to change it, but I found none.</p>

<p>Can this feature (though it's more like a bug to me) be disabled?</p>

The way to select a startup project is described in
Sara Ford's blog "Visual Studio Tip of the Day
" (highly recommended). She has a post there about
setting up StartUp projects
. Essentially there are 2 ways, the easiest one being right-clicking on the desired project, and choosing "Set As StartUp Project". That prevents other projects from becoming the StartUp project, even if you click on one their files.