> DataFrame("1-1" = 1, check.names =  FALSE)[rep("1-1", 1)]
DataFrame with 1 row and 1 column
        1-1
  <numeric>
1         1

> DataFrame("1-1" = 1, check.names =  FALSE)[rep("1-1", 2)]
DataFrame with 1 row and 2 columns
       X1.1      X1.1
  <numeric> <numeric>
1         1         1

Thanks, fixed for the next release.