title: Unrecognized column name after loading data table with fread
body: <p>I load a data table with <code>fread</code> the way I always do.  The files has ~2M records and is tab delimited.</p>
  
  <p>The load is successful.  I can print the head of the table and the column names, so far so good.</p>
  
  <p>But then either changing the name of the <strong>first column</strong> or setting it as a key fails complaining it <strong>cannot find the <em>old</em> column name</strong>.  I am sure there is no typo in the column name, no heading or trailing space, I tried many times with copy/paste and retyping.  I can change the name of apparently any other column.</p>
  
  <p>The first column is long integer id's, so I had to load the bit64 package to get rid of a warning in 'fread', but it did not seem to help.  Is it a clue?</p>
  
  <p>Does anyone have any idea what could cause such a symptom?  How to debug?</p>
  
  <p>I use R 3.1.0 on Windows 64, latest version of all packages.</p>
  
  <p>Edit: more details</p>
  
  <p>The data load command:</p>
  
  <p><code>txnData &lt;- fread(txnInDataPathFileName, header=TRUE, sep="\t", na.strings="NA")</code></p>
  
  <p>The column names:</p>
  
  <pre><code>colnames(txnData)
   [1] "txn_ext_id"  "txn_desc"       "txn_type_id"    "site_id"        "date_id"        "device_id"      "cust_id"       
   [8] "empl_id"        "txn_start_time" "txn_end_time"   "total_sales"    "total_units"    "gross_margin"
  </code></pre>
  
  <p>The rename column that fails (and so does setkey):</p>
  
  <pre><code>setnames(txnData, "txn_ext_id", "txnId")
  Error in setnames(txnData, "txn_ext_id", "txnId") : 
    Items of 'old' not found in column names: txn_ext_id
  </code></pre>
  
  <p>And finally the requested dput command:</p>
  
  <pre><code>dput(head(txnData))
  structure(list(`txn_ext_id` = structure(c(4.88536962440272e-311, 
  1.10971996159584e-311, 9.9460266389845e-312, 1.0227644072435e-311, 
  1.10329710699982e-311, 1.01930594588518e-311), class = "integer64"), 
      txn_desc = c("checkout transaction", "checkout transaction", 
      "checkout transaction", "checkout transaction", "checkout transaction", 
      "checkout transaction"), txn_type_id = c(0L, 0L, 0L, 0L, 
      0L, 0L), site_id = c(982L, 982L, 982L, 982L, 982L, 982L), 
      date_id = c("2012-12-24", "2013-11-27", "2013-04-08", "2013-06-04", 
      "2013-11-14", "2013-05-28"), device_id = c(8L, 7L, 8L, 53L, 
      8L, 5L), cust_id = structure(c(2.02600292130833e-313, 2.02572944866119e-313, 
      2.02583815970388e-313, 2.02580527009968e-313, 2.02568405005593e-313, 
      2.02736582767668e-313), class = "integer64"), empl_id = c("?", 
      "?", "?", "?", "?", "?"), txn_start_time = c("2012-12-24T08:35:56", 
      "2013-11-27T12:43:30", "2013-04-08T11:48:29", "2013-06-04T15:27:47", 
      "2013-11-14T12:57:38", "2013-05-28T11:03:21"), txn_end_time = c("2012-12-24T08:38:00", 
      "2013-11-27T12:47:00", "2013-04-08T11:49:00", "2013-06-04T15:35:00", 
      "2013-11-14T13:00:00", "2013-05-28T11:05:00"), total_sales = c(48.86, 
      69.7, 8.53, 33.46, 39.19, 35.56), total_units = c(12L, 44L, 
      3L, 4L, 14L, 17L), gross_margin = c(0, 0, 0, 0, 0, 0)), .Names = c("txn_ext_id", 
  "txn_desc", "txn_type_id", "site_id", "date_id", "device_id", 
  "cust_id", "empl_id", "txn_start_time", "txn_end_time", "total_sales", 
  "total_units", "gross_margin"), class = c("data.table", "data.frame"
  ), row.names = c(NA, -6L), .internal.selfref = &lt;pointer: 0x00000000002c0788&gt;)
  </code></pre>