Package update conflict between two developers

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Oracle

I am working in a database with another developer creating packages. I made a changes on a procedure within a package and he did not see the changes that I performed on the procedure within the package. So, he did not think that I had made the changes. The other developer made the changes to the same packages. Both his and my changes were there until I close the database on my machine. When I re open the machine my changes were missing. We both rebuild the package but neither of us saw the changes. He has a 2012 version of oracle client and mind is a new version of 2014. Can there be and issue with the fact that we both have different version install on our machine. Give me some feedback on what the best approach to developing with multiple developer on different version of Oracle when creating multiple procedure in the same package.