title: XTS replacement error NextMethod(.Generic) : number of items to replace
body: <p>I'm struggling with xts right now... I have an XTS object, and I am trying to replace a specific date's data with a new set, but I keep running into issues of replacement length, even though I am certain they are the same and no missing data. Any ideas?</p>
  
  <p>I made a dummy example to demonstrate my issues:</p>
  
  <pre><code>R&gt; test1 = xts(cbind(trade_level = 1, t2 = 3),order.by=as.Date("1991-01-02"))
  R&gt; test2 = xts(cbind(trade_level = 5, t2 = .053),order.by=as.Date("1991-01-02"))
  R&gt; first_day = "1991-01-02"
  R&gt; test1[first_day] = test2
  Warning message:
  In NextMethod(.Generic) :
    number of items to replace is not a multiple of replacement length
  R&gt; sessionInfo()
  R version 3.0.1 (2013-05-16)
  Platform: x86_64-w64-mingw32/x64 (64-bit)
  
  locale:
  [1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
  [3] LC_MONETARY=English_United States.1252 LC_NUMERIC=C                          
  [5] LC_TIME=English_United States.1252    
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  other attached packages:
  [1] reshape2_1.2.2  xts_0.9-7       zoo_1.7-10      ggplot2_0.9.3.1
  
  loaded via a namespace (and not attached):
   [1] colorspace_1.2-4   dichromat_2.0-0    digest_0.6.4       grid_3.0.1        
   [5] gtable_0.1.2       labeling_0.2       lattice_0.20-23    MASS_7.3-29       
   [9] munsell_0.4.2      plyr_1.8           proto_0.3-10       RColorBrewer_1.0-5
  [13] scales_0.2.3       stringr_0.6.2      tools_3.0.1       
  </code></pre>