Multiindex slicing df.loc[idx[dim1,dim2,dim3],:] not working right in some cases
#### Code Sample, a copy-pastable example if possible

```
import pandas as pd
import numpy as np
np.random.seed(0) 
idx = pd.IndexSlice
midx = pd.MultiIndex.from_product([['CS'], range(20), range(-1100, 6000)]) 
df = pd.DataFrame(np.random.randn(7100*20, 3), columns=['dat1', 'dat2', 'dat3'], index=midx)
```
#### Output

```
> df.loc[idx['CS', :, -1000:-950], :].head()
                dat1      dat2      dat3
CS 0 -1000 -1.306527  1.658131 -0.118164
     -999  -0.680178  0.666383 -0.460720
     -998  -1.334258 -1.346718  0.693773
     -997  -0.159573 -0.133702  1.077744
     -996  -1.126826 -0.730678 -0.384880
```

```
> df.loc[idx['CS', :, -1000:-50], :].head()
                dat1      dat2      dat3
CS 0 -1100  1.764052  0.400157  0.978738  # <<< Index Level 2 should start at -1000
     -1099  2.240893  1.867558 -0.977278
     -1098  0.950088 -0.151357 -0.103219
     -1097  0.410599  0.144044  1.454274
     -1096  0.761038  0.121675  0.443863
```
#### output of `pd.show_versions()`
## INSTALLED VERSIONS

commit: None
python: 3.5.1.final.0
python-bits: 64
OS: Linux
OS-release: 3.16.0-59-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8

pandas: 0.18.0
nose: 1.3.7
pip: 8.1.1
setuptools: 20.2.2
Cython: 0.23.4
numpy: 1.10.4
scipy: 0.17.0
statsmodels: 0.6.1
xarray: None
IPython: 4.0.3
sphinx: 1.3.5
patsy: 0.4.0
dateutil: 2.4.2
pytz: 2015.7
blosc: None
bottleneck: 1.0.0
tables: 3.2.2
numexpr: 2.4.6
matplotlib: 1.5.1
openpyxl: 2.3.2
xlrd: 0.9.4
xlwt: 1.0.0
xlsxwriter: 0.8.4
lxml: 3.5.0
bs4: 4.4.1
html5lib: None
httplib2: None
apiclient: None
sqlalchemy: 1.0.11
pymysql: None
psycopg2: None
jinja2: 2.8
boto: 2.39.0
