file system ownership discrepancy between fedora 15 and fedora 19

[Ozgur Bas]

Hi,
I have been using old version of OS s fedora 15 and  red hat 6.2.
Hdd partitions made by red hat seen by fedora 15 successfully, despite 
using different usernames of OSs.
I have installed to try fedora 19 kde in an other machine.
The case was any hdd partition made by redhat 6.2(which was usable in 
fedora15) is not accessible on fedora 19 machine.
And also, any hdd partition made by fedora 19 is not accessible by 
redhat6.2 and fedora15.

What is the problem with ownership management of OS versions?
Any solution?