I caught this in #140 but have not yet discovered the cause of the problem.

> num <- labelled(c(1, 2), c(a = 1, b = 3))
> num
<Labelled>
[1] 1 2

Labels:
 value label is_na
     1     a FALSE
     3     b FALSE
> roundtrip_var(num)
<Labelled>
[1] 1 2

Labels:
 value label is_na
     0     a FALSE
     0     b FALSE

I opened the file in Stata and verified that the labels are not written correctly:

. label list
x..i..:
           0 a
           0 b

It might be a bug in ReadStat, since the label-writing code in DfWriter seems to be basically the same as the code for integer labelleds, which do work fine.