DATEVALUE() gives different values for similar data
Dates in Excel are stored as integers. While you have been confused by how it is displayed in the cell, the value your function returns is indeed the correct one, you just have to change the formatting of the cell to the same as the other one, and they should display the same value.
If you have a look at the dropdown-menu for the format of the cell, you can see that the two are the same:
In Excel a date is always a numeric value. 10 Jun 2015 is 42165.
You have to change the column format to date. I guess you are using General or Number.