Infinite loop in Python when doing simple operations
Hi there,

I have a ginormous problem right now.

When doing simple operations, a python interpreter subprocess keeps running in the background (even when my application finished) and eats a lot of CPU (25%) continually, and forever.

It seems that whenever I do some simple operations, such as:

```
df / serie2
df.div(serie2)
df - serie2
df - 2
df.apply(minus)
df ** 2
```

where minus is:

```
def minus(serie):
    serie - serie2
```

But the following operations do not produce the bug:

```
df * (1.0/serie2)
df * serie2**-1
df * df
```

And any operation using \* is typically not affected by the bug.

The bug is that if the above operations are present in my code, it launches an instance of Python and then this instance never goes away, and keeps using 25 percent of my CPU!

I am using:
Windows 7 x64
Python 2.7
Pandas 0.11 rc1
Numpy 1.7.1
IPython 0.13.2

What is weird is that I have a hard time reproducing it outside of my application (ie: directly inside IPython with simplified code), so I can't really post anything here.

Another thing to note is that when this bug happens compared to when it doesn't (using the workarounds I outlined above by replacing buggy operations by non buggy operations, and having the same result at the end), not only a python subprocess keeps running in the background, but also while my application is running, my app use a LOT more CPU and memory (CPU ~ 60% when buggy, ~10-20% when not buggy).

I'm still trying to debug the problem, but it seems it can't be profiled (because it's not a loop due to my application, my application ends correctly, and then the Python sub-process keeps processing something but I can't know what!).

If someone has an idea to help me debugging I would gladly hear your ideas. Meanwhile this is posted here as a reference if anyone else gets a similar problem.
