BUG?: Runtime Warning  invalid value encountered in greater has_large_values
When I try and run `head()` or `query()` on a dataframe while working in ipython, I'm getting the following error on a DataFrame that seems pretty normal (850 rows, 159 columns, mixed type (lots of strings). 

```
/Users/Nick/github/pandas/pandas/core/format.py:2052: RuntimeWarning: invalid value encountered in greater has_large_values = (abs_vals > 1e8).any()
/Users/Nick/github/pandas/pandas/core/format.py:2053: RuntimeWarning: invalid value encountered in less  has_small_values = ((abs_vals < 10 ** (-self.digits)) &
/Users/Nick/github/pandas/pandas/core/format.py:2054: RuntimeWarning: invalid value encountered in greater (abs_vals > 0)).any()
```

Oddly, it comes up _before_ i finish the command or hit enter, and I can still run the command if I type it out in an editor and execute the line -- it only comes up when I'm typing interactively. 

Is this a bug? If not, any idea what it is? Not sure how to recreate with other data. 
