Safari issue not loading image on portfolio detailpage

[bizztools]

We have a big issue on our website: http://dedrukweg.be.testbyte.nl/portfolio/geboortekaartjes/
In all browsers portfolio detail pages are loading fine but in safari the image on the portfolio detail pages is not loading. Not on workstation, not on tablet, ..

Once you switch to other application an come back to the browser the image is there.

Is this a known issue in your theme and how can we fix this ?

kind Regards

Ticket