On AIX, if log_subcmds is enabled, becoming another user does not get proper environment.  For example, the following sequence:

sudo -i
su - otheruser
vi testfile

This will throw an error - "History file has no read permission"

Output from truss shows vi attempting to read //.vi_history instead of .vi_history from the user.

This can also be seen via output from the "env" command.  Root's path is still in place instead of otherusers.  

Behavior works as expected if log_subcmds is not enabled.