Question on file permissions

Hi there,

today I saw something on my system that kind of puzzeles me.

When creating a new file as one user (say "User_A"), then the file is owned by User_A and the group staff. As seen when doing an ls -la:

drwxr-xr-x 2 User_A staff 68 16 Jul 23:11 testing

Now when I log out and log back in as another user, say User_B and I do a la -la on the same file, I see that the file is suddenly owned by User_B:

drwxr-xr-x 2 User_B staff 68 16 Jul 23:11 testing

How is that even possible? Is the file ownership dynamically assigned to whatever user is logged in? I don't get it. Any ideas?

Thanks