pandas.DataFrame.apply function calls func twice on the first column/row
#### Code Sample, a copy-pastable example if possible

```python
addDf.apply(lambda x:addCredit(x['content_name'],x['content_value'],x['credit'],userCreditSession,creditAction,queryDate,creditReason,creditType),axis=1)
```
#### Problem description
In my code ,I want to use apply to add credit for some credit object.In the pandas.DataFrame.apply
function notes,it says "In the current implementation apply calls func twice on the first column/row to decide whether it can take a fast or slow code path.".But when I tried this function,I found not only the 
first column/row calls func twice. It calls func twice on the head 3 columns/rows.

execute result as below:
select score,date from xx.xxx where credit_object = '0.1.0c883dfe72da252ea181ab6ce5a1f22a.c9a6dc'
select score,date from xx.xxx where credit_object = '0.1.0ed09a1a5cd60674146b6b3e0315b919.9d983b'
select score,date from xx.xxx where credit_object = '0.0.c222af7998f36fe34e4cf82b4d879dc6.8d8583'
select score,date from xx.xxx where credit_object = '0.1.0c883dfe72da252ea181ab6ce5a1f22a.c9a6dc'
select score,date from xx.xxx where credit_object = '0.1.0ed09a1a5cd60674146b6b3e0315b919.9d983b'
select score,date from xx.xxx where credit_object = '0.0.c222af7998f36fe34e4cf82b4d879dc6.8d8583'
select score,date from xx.xxx where credit_object = '0.0.2bfe2fdaf657bd1f9339a6f9542919df.10e946'

code execute environment:
centos 6.4
python 2.7
pandas version: 0.19.2

look forward to your replying,many thanks!