Scenario: In previous versions of Word, you may have been able to access the View.SplitSpecial value to verify if the Reviewing Pane is open. However, in Word 2013, View.SplitSpecial returns 0 whether the Reviewing Pane is open or closed. Additionally, View.SplitSpecial can still be set to the value wdPaneRevisions through the Object Model, which will continue to open the Reviewing Pane.
Cause: Prior to Word 2013, another pane could not be opened at the same time as the Reviewing Pane. However, the behavior was changed such that Reviewing Pane can be opened in addition to another pane (this is similar to how the Navigation Pane works). From the perspective of the product team, it did not make sense to return the wdPaneRevisions value if another pane could be opened as well.
Solution: A workaround for this scenario in Word 2013 is to access the Revisions index in the CommandBars object, and check the Visible property to determine if the Revisions pane is open (True means it is open, False means it is closed). An example of this can be seen as such:
Sub AlertRevisionStatus()
If CommandBars("Revisions").Visible = True Then
MsgBox("Reviewing Pane is open.")
Else
MsgBox("Reviewing Pane is closed.")
End If
End Sub
At the time of writing, the MSDN article on the View.SplitSpecial property has not yet been updated to reflect this change in Word 2013.