fnd_global.Org id gets reset in concurrent processing under request set

Hi,

We have a group of programs runs in request
set. These programs access same package procedure with different input
parameters.

Each program set fnd_global.apps_initialize() to
apps initialize the package procedure with different user, responsibility
etc., based on input parameters being passed.

We observed some time, after setting OU to some
value it gets changed to another value in same session.

Is it because when concurrent programs
run under requests set, they interferes the parallel running
programs sessions? Pl suggests.

Thanks!