The method was introduced in commit 43f57d3f31117c7677d23f1477a4579b1b562c67, ending with the following return statement:

return (it == end) ? false : (*it)->filePath() != filename;

I believe this is incorrect, since we are looking for a match. In other words the statement should be as follows:

return (it == end) ? false : (*it)->filePath() == filename;

This mistake also causes ProjectExplorer::SessionManager::projectForFile() to work incorrectly (i.e. now it returns the first project from the list which actually does not contain the file).