I have a ISO image (ISO_1.iso) which contain just one file - another ISO image (ISO_2.iso)!

When I mount ISO_1.iso - I see the CONTENTS of ISO_2.iso - not ISO_2.iso as a FILE!

Code:
ISO_1.iso        <---- Image mounted
 --> ISO_2.iso   <---- Expected contents
  ---> my_files  <---- Actual contents
Is this a bug? Mounting ISO_1.iso in ISObuster is correct.