The issue still remains, but the behavior was changed.
Test environment: unity - unity 4.20.0-0ubuntu2
Scenario one
1) Click exactly one application icon in Unity Launcher, Firefox, for example.
2) Minimize Firefox
3) Click Firefox icon in Unity Launcher.
3) Result: Firefox could not be restored.
Scenario two
1) Click two application icons in Unity Launcher, Firefox and Software Center, for example.
2) Minimize Software Center, then Firefox.
3) Click Firefox icon in Unity Launcher.
3) Result: Firefox will be restored.
The issue still remains, but the behavior was changed.
Test environment: unity - unity 4.20.0-0ubuntu2
Scenario one
1) Click exactly one application icon in Unity Launcher, Firefox, for example.
2) Minimize Firefox
3) Click Firefox icon in Unity Launcher.
3) Result: Firefox could not be restored.
Scenario two
1) Click two application icons in Unity Launcher, Firefox and Software Center, for example.
2) Minimize Software Center, then Firefox.
3) Click Firefox icon in Unity Launcher.
3) Result: Firefox will be restored.