We have tested your sites and found that the revolution slider is overriding the default wordpress behavior by processing on the images on the fly, not sure of the reason why the plugin is doing that.
We created a test page on both pages and added icon box to it and uploaded a new image and the icon box is working perfectly but once we your revolution slider to this page the iconbox images are ruined.
@klar: You have a problem in a slider named “Klar” and “Klar1” Please try the following to make sure from what i’m saying:
1- Add your Slider “Coffee” to the homepage and upload a new image to the icon box and check, you will find that it is working normally, now replace that slider with “Klar” and you will find the icon ruined again
Most probably there is a setting in the revolution slider and we are currently investigating it, for now try to redo your sliders with the basic settings and re-upload your images and it will work properly