Plotting dataframe: vertical gridlines not shown
Tried to plot a specific DataFrame: but the vertical gridlines are not showing up:

My setup:

``` python
In [1]: import pandas as pd
In [2]: import numpy as np
In [3]: import matplotlib
In [4]: import sys
In [5]: %matplotlib inline
In [6]: sys.version
Out [6]: '3.5.1 |Anaconda 2.4.1 (64-bit)| (default, Dec  7 2015, 15:00:12) [MSC v.1900 64 bit (AMD64)]'
In [7]: np.__version__
Out[7]: '1.10.1'
In [8]: matplotlib.__version__
Out [8]: '1.5.1'
In [9]: pd.__version__
Out [9]: '0.17.1'
```

If i try to plot a random dataFrame it works as expected:

``` python
In [10]: N = 2000
In [11]: df = pd.DataFrame(np.random.randn(N, 5), index=pd.date_range('1/1/1975', periods=N))
In [12]: df.plot(grid=True)
```

![randomdataframe](https://cloud.githubusercontent.com/assets/16588610/12289820/e753ac4e-b9dd-11e5-946b-494aec603451.png)

But if i try to plot the dataframe contained in the zip
[plot_xgrid_error.zip](https://github.com/pydata/pandas/files/88600/plot_xgrid_error.zip)
i get the following without vertical grid lines:

``` python
In [13]: data = pd.read_hdf(r'plot_xgrid_error.h5', 'data')
In [14]: data.plot(grid=True)
```

![specialdataframe](https://cloud.githubusercontent.com/assets/16588610/12289909/add98708-b9de-11e5-9519-3bd360061830.png)

May somebody can help me?
Why the vertical grid lines not showing up?
Is it supposed to do so?
Found something similar here #11076
