[R] Cannot get "==" operator to return TRUE

[G See]

I have a data.frame named "df". The dput of df is at the bottom of this e-mail.
What I'd like to do is replace the "n/a " values with NA.  On Mac OSX, it works
to do this:
df[df == "n/a"] <- NA

However, it does not work on Ubuntu.  See below.

Thanks in advance,
Garrett

> x <- df[27, 4] # complete data.frame dput is below
> dput(x)
"n/a "
> x == "n/a "
[1] FALSE
> x == "n/a"
[1] FALSE
> str(x)
 chr "n/a "
> is.na(x)
[1] FALSE
> grep("n/a ", x)
integer(0)
> grep("n/a", x)
[1] 1


> sessionInfo()
R version 2.14.1 (2011-12-22)
Platform: x86_64-pc-linux-gnu (64-bit)

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
 [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8
 [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8
 [7] LC_PAPER=C                 LC_NAME=C
 [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base

other attached packages:
[1] XML_3.4-3                  qmao_1.1.10
[3] FinancialInstrument_0.10.9 quantmod_0.3-17
[5] TTR_0.21-0                 Defaults_1.1-1
[7] xts_0.8-3                  zoo_1.7-6

loaded via a namespace (and not attached):
[1] grid_2.14.1    lattice_0.20-0 tools_2.14.1
>


### More detail ###
## Here is the complete data.frame
> dput(df)
structure(list(SYMBOL = c("GOOG ", "GOOG ", "GOOG ", "GOOG ",
"GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ",
"GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ",
"GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG ",
"GOOG ", "GOOG ", "GOOG ", "GOOG ", "GOOG "), PERIOD = c("Q4 2011",
"Q3 2011", "Q2 2011", "Q1 2011", "Q4 2010", "Q3 2010", "Q2 2010",
"Q1 2010", "Q4 2009", "Q3 2009", "Q2 2009", "Q1 2009", "Q4 2008",
"Q3 2008", "Q2 2008", "Q1 2008", "Q4 2007", "Q3 2007", "Q2 2007",
"Q1 2007", "Q4 2006", "Q3 2006", "Q2 2006", "Q1 2006", "Q4 2005",
"Q3 2005", "Q2 2005", "Q1 2005", "Q4 2004", "Q3 2004"),
    `EVENT TITLE` = c("Q4 2011 Google Earnings Release", "Q3 2011
Google Inc Earnings Release",
    "Q2 2011 Google Inc Earnings Release", "Q1 2011 Google Inc
Earnings Release",
    "Q4 2010 Google Earnings Release", "Q3 2010 Google Earnings Release",
    "Q2 2010 Google Earnings Release", "Q1 2010 Google Earnings Release",
    "Q4 2009 Google Earnings Release", "Q3 2009 Google Earnings Release",
    "Q2 2009 Google Earnings Release", "Q1 2009 Google Earnings Release",
    "Q4 2008 Google Earnings Release", "Q3 2008 Google Earnings Release",
    "Q2 2008 Google Earnings Release", "Q1 2008 Google Earnings Release",
    "Q4 2007 Google Earnings Release", "Q3 2007 Google Earnings Release",
    "Q2 2007 Google Earnings Release", "Q1 2007 Google Earnings Release",
    "Q4 2006 Google Earnings Release", "Q3 2006 Google Earnings Release",
    "Q2 2006 Google Earnings Release", "Q1 2006 Google Earnings Release",
    "Q4 2005 Google Earnings Release", "Q3 2005 Google Earnings Release",
    "Q2 2005 Google Earnings Release", "Q1 2005 Google Earnings Release",
    "Q4 2004 Google Earnings Release", "Q3 2004 Google Earnings Release"
    ), `EPS ESTIMATE` = c("$ 10.49 ", "$ 8.74 ", "$ 7.85 ",
    "$ 8.10 ", "$ 8.09 ", "$ 6.68 ", "$ 6.52 ", "$ 6.60 ",
    "$ 6.50 ", "$ 5.42 ", "$ 5.09 ", "$ 4.93 ", "$ 4.95 ",
    "$ 4.76 ", "$ 4.74 ", "$ 4.52 ", "$ 4.44 ", "$ 3.78 ",
    "$ 3.59 ", "$ 3.30 ", "$ 2.92 ", "$ 2.42 ", "$ 2.22 ",
    "$ 1.97 ", "n/a ", "n/a ", "n/a ", "n/a ", "n/a ",
    "n/a "), `EPS ACTUAL` = c("$ 9.50 ", "$ 9.72 ", "$ 8.74 ",
    "$ 8.08 ", "$ 8.75 ", "$ 7.64 ", "$ 6.45 ", "$ 6.76 ",
    "$ 6.79 ", "$ 5.89 ", "$ 5.36 ", "$ 5.16 ", "$ 5.10 ",
    "$ 4.92 ", "$ 4.63 ", "$ 4.84 ", "$ 4.43 ", "$ 3.91 ",
    "$ 3.56 ", "$ 3.68 ", "$ 3.18 ", "$ 2.62 ", "$ 2.49 ",
    "$ 2.29 ", "n/a ", "n/a ", "n/a ", "n/a ", "n/a ",
    "n/a "), `PREV. YEAR ACTUAL` = c("$ 8.75 ", "$ 7.64 ",
    "$ 6.45 ", "$ 6.76 ", "$ 6.79 ", "$ 5.89 ", "$ 5.36 ",
    "$ 5.16 ", "$ 5.10 ", "$ 4.92 ", "$ 4.63 ", "$ 4.84 ",
    "$ 4.43 ", "$ 3.91 ", "$ 3.56 ", "$ 3.68 ", "$ 3.18 ",
    "$ 2.62 ", "$ 2.49 ", "$ 2.29 ", "n/a ", "n/a ", "n/a ",
    "n/a ", "n/a ", "n/a ", "n/a ", "n/a ", "n/a ", "n/a "
    ), TIME = c("2012-01-19 15:15:00 CST", "2011-10-13 15:15:00 CDT",
    "2011-07-14 15:15:00 CDT", "2011-04-14 15:15:00 CDT", "2011-01-20
15:15:00 CST",
    "2010-10-14 15:15:00 CDT", "2010-07-15 15:15:00 CDT", "2010-04-15
15:15:00 CDT",
    "2010-01-21 15:15:00 CST", "2009-10-15 15:15:00 CDT", "2009-07-16
15:15:00 CDT",
    "2009-04-16 15:15:00 CDT", "2009-01-22 15:15:00 CST", "2008-10-16
15:15:00 CDT",
    "2008-07-17 15:15:00 CDT", "2008-04-17 15:15:00 CDT", "2008-01-31
15:15:00 CST",
    "2007-10-18 15:15:00 CDT", "2007-07-19 15:15:00 CDT", "2007-04-19
15:15:00 CDT",
    "2007-01-31 15:15:00 CST", "2006-10-19 15:15:00 CDT", "2006-07-20
15:15:00 CDT",
    "2006-04-20 15:15:00 CDT", "2006-01-31 15:15:00 CST", "2005-10-20
15:15:00 CDT",
    "2005-07-21 15:15:00 CDT", "2005-04-21 15:15:00 CDT", "2005-02-01
15:15:00 CST",
    "2004-10-21 15:15:00 CDT")), .Names = c("SYMBOL", "PERIOD",
"EVENT TITLE", "EPS ESTIMATE", "EPS ACTUAL", "PREV. YEAR ACTUAL",
"TIME"), row.names = 2:31, na.action = structure(31L, .Names = "32",
class = "omit"), class = "data.frame")