stop pd.DataFrame.from_csv() from converting integer index to date

pandas.DataFrame.from_csv(filename) seems to be converting my integer index into a date.

This is undesirable. How do I prevent this?

The code shown here is a toy version of a larger problem. In the larger problem, I am estimating and writing the parameters of statistical models for each zone for later use. I thought by using a pandas dataframe indexed by zone, I could easily read back the parameters. While pickle or some other format like json might solve this problem I'd like to see a pandas solution....except pandas is converting the zone number to a date.

#!/usr/bin/python

cache_file="./mydata.csv"

import numpy as np
import pandas as pd
zones = [1,2,3,8,9,10]

def create():
    data = []
    for z in zones:
        info = {'m': int(10*np.random.rand()), 'n': int(10*np.random.rand())}
        info.update({'zone':z})
        data.append(info)
    df = pd.DataFrame(data,index=zones)
    print "about to write this data:"
    print df
    df.to_csv(cache_file)

def read():
    df = pd.DataFrame.from_csv(cache_file)
    print "read this data:"
    print df

create()
read()

Sample output:

about to write this data:
    m  n  zone
1   0  3     1
2   5  8     2
3   6  4     3
8   1  8     8
9   6  2     9
10  7  2    10

read this data:
            m  n  zone
2013-12-01  0  3     1
2013-12-02  5  8     2
2013-12-03  6  4     3
2013-12-08  1  8     8
2013-12-09  6  2     9
2013-12-10  7  2    10

The CSV file looks OK, so the problem seems to be in reading not creating.

mydata.csv

,m,n,zone
1,0,3,1
2,5,8,2
3,6,4,3
8,1,8,8
9,6,2,9
10,7,2,10

I suppose this might be useful:

pd.__version__
0.12.0

Python version is python 2.7.5+

I want to record the zone as an index so I can easily pull out the corresponding parameters later. How do I keep pandas.DataFrame.from_csv() from turning it into a date?