[Regression 5.4.2] Some gif images on websites will not load, at least the first time

Since the migration to Qt 5.4.2 (and I beleive libpng update, but dont know if it's related because they are gif images), some gif doesn't load the first time a page is loaded when using QtWebkit.

Sometimes reloading the page will finally load the gif, sometimes not.

This can be reproduce with Tab Browser example (WebKit version), on this french banque website : https://particuliers.societegenerale.fr/

1 - In the red box on top right corner, tap any dummy number (e.g. 12345678), click on Ok
2 - See the box having some problem loading some gif images.
3 - Close the box with keypad and click Ok again, the gif images normally load properly.

See image attached, also some other gif doesn't succeed to load on this page, but the behavior is random.