Export > Start date and End Date are not working properly on billing data file

Start date and End Date are not working properly on billing data file for which new JIRA is created

below are some observations found when tried putting different dates in start date and end date fields on template settings page.

1) 07/01/2016 to 07/31/2016
One record exported with the above mentioned date span

2) 06/01/2016 to 06/30/2016
Six records exported for months from Jan 2016 to June 2016

3) 05/01/2016 to 05/31/2016
Seventeen records exported for months from Jan 2015 to May 2016

4) 04/01/2016 to 04/30/2016
Four records exported for months from Jan 2016 to April 2016

5) 03/01/2016 to 03/31/2016
Three records exported for months from Jan 2016 to March 2016

6) 01/01/2016 to 07/31/2016
Nineteen (19) records exported for months from Jan 2015 to July 2016

Can you please check what is causing these date differences in exported billing data file ? Only 1st observation for July month was as per mentioned date span compared to others.