Images under Sub menu with visibility:hidden does not not loads lazily

In our application home page, we have menu bar on which customer can hover and sub Menu become visible and we are showing some images in our some menu.
But I can see even before hovering on the menu bar, the sub menu images already loaded(Verified in the network tab).

In every other places it is working fine only on sub menu images it loading eagerly instead of lazily.

Can some one give me some hint, where can be the problem?