Juno by default doesn’t present the MRU (Most Recently Used) tab behaviour that you see in Indigo (it never worked quite right) and instead uses the Editor document order.
I believe you can re-activate it be either switching to the Classic theme in Preferences>General>Appearance or by editing the CSS. See http://wiki.eclipse.org/Eclipse4/CSS
.MPartStack {
swt-mru-visible: true;
}
Don’t forget to restart Eclipse to make it use the new parameters.