title: ggplot2 draws two legends
body: <p>I have almost complete the following graph, but there is one problem with it. </p>
  
  <p>The legend in the graph is drawn twice. </p>
  
  <p>Here is the data:</p>
  
  <pre><code>structure(list(Period = c("January 1997 - August 2003", "September 2003 - Jun 2005", 
  "Jul 2005 - Dec 2009", "January 1997 - August 2003", "September 2003 - Jun 2005", 
  "Jul 2005 - Dec 2009"), Time.Period = structure(c(1L, 3L, 2L, 
   1L, 3L, 2L), .Label = c("Jan 1997 - Aug 2003", "Jul 2005 - Dec 2009", 
   "Sep 2003 - Jun 2005"), class = "factor"), Variable = structure(c(2L, 
   2L, 2L, 1L, 1L, 1L), .Label = c("Significant", "Zscore"), class = "factor"), 
   Score = c(8.798129, 4.267268, 7.280275, 1.64, 1.64, 1.64)), .Names = c("Period", 
   "Time.Period", "Variable", "Score"), class = "data.frame", row.names = c(NA, 
   -6L))
  
  ggplot(glomor, aes(x=Time.Period, y=Score, group=Variable, shape=Variable, color=Variable)) +
   geom_point() +
   guides(fill=FALSE) +
   scale_x_discrete(limits=c("Jan 1997 - Aug 2003","Sep 2003 - Jun 2005","Jul 2005 - Dec 2009"),    expand=c(.08,0)) +
    geom_line(aes(linetype=Variable), size=1.5) +
    geom_point(size=4.2) +
    scale_linetype_manual(values=c(1,3)) +
    scale_color_manual(values=c("black", "grey40"), name="", labels=c("Signficant Z-Score",   "Moran's I Z-Score")) +
    scale_fill_discrete(name="", label=c("Signficant Z-Score", "Moran's I Z-Score")) +
    theme_classic()+
    ylim(0,10) +
    xlab("Time Periods") +
    ylab("Moran's I Z-Score") +
    theme(axis.title.x=element_text(size=14)) +
    theme(axis.title.y=element_text(size=14)) +
    theme(legend.position=c(.75, .85)) +
    theme(legend.background = element_rect(fill="white")) +
    theme(legend.key = element_blank())
  </code></pre>
  
  <p>Does anyone know, why the ggplot2 produces two legends? </p>