ASE read/write lammps-data

Does anyone know why, when I use ASE to read a lammps-data file then write a lammps-data file the atom type order is changing? E.g. atom type 1 is now atom type 2 via. Is this a bug?

python:

from ase import Atoms
from ase.io import read, write

structure = read('in.data', format='lammps-data')
write('out.data', structure, format='lammps-data')

in.data

LAMMPS data file

10 atoms
2 atom types

0.23804174467495384 19.491958255325184 xlo xhi
0.07381357606622793 19.656186423933754 ylo yhi
0 56.5 zlo zhi

Masses

1 58.6934
2 92.90637

Atoms # atomic

1 1 8.003396981729855 7.81701149126033 1.0535209764894955
2 1 1.8544555442034365 9.172670309685868 0.9556990920000298
3 1 1.262386194517821 3.2102360277389073 4.213469056491476
4 1 4.8380939404195145 5.400518571434123 2.0481053818579635
5 **2** 0.728965153670273 0.6672645065312569 3.9828521945241757
6 1 2.938540565890799 1.7292699978079278 5.562830039925194
7 1 5.209963031033449 5.0870854851364395 4.450506459379925
8 1 2.1052031130812727 5.7946319616994115 3.615858097320411
9 **2** 3.0238292680411685 4.424244277205381 5.820017273188103
10 1 1.640326666016647 2.486739609699881 1.8653504759274637

out.data

(written by ASE)

10 atoms
2 atom types

0.0      19.253916510650228  xlo xhi
0.0      19.582372847867525  ylo yhi
0.0                    56.5  zlo zhi

Atoms # atomic

     1   2      8.0033969817298534      66.564130034862913      1.0535209764894955
     2   2     -75.161210498397466      28.755043157553395     0.95569909200002978
     3   2     -56.499363337432854      3.2102360277389073      4.2134690564914763
     4   2     -33.669739080880937      24.982891419301648      2.0481053818579635
     5 **1**     -37.778867867630176      39.832010202266304      3.9828521945241757
     6   2      2.9385405658907984      21.311642845675451      5.5628300399251938
     7   2     -33.297869990267003     -34.077660210598609      4.4505064593799251
     8   2     -17.148713397568955     -52.952486581903159      3.6158580973204111
     9   **1**       3.023829268041168      24.006617125072907      5.8200172731881032
    10   2      20.894243176666873      22.069112457567407      1.8653504759274639