Xcode: changing double clicking file behavior

One of my projects suddenly had its double-clicking behavior changed and I don't know how to change it back.

The behavior I want:

Double clicking a source code file opens up a new window.

The behavior I have:

Double clicking a source code file opens the file in the existing window. This results in only allowing one window open for the project at any time.

Needless to say this is a bit frustrating. I can't find any preference that seems to control this. It seems to be a per-project preference (it is only happening in one project). Any ideas?

Note: I am using the condensed layout.

Note 2: "Open in Separate Editor" does not work.

From stackoverflow

• Ahh,

  Found the answer. There is a button in the ToolBar of the editor window that says "Grouped" or "Ungrouped".

  If it says "Grouped" then files open in the same window.

  If it says "Ungrouped" then files open in new windows.

  Found the answer here:

  http://meandmarkpublishing.blogspot.com/2007/06/reducing-xcodes-window-clutter.html