Moving the view by dragging the map with the mouse is broken on http://mapy.cz/. Clicking for zooming and mouse wheel for zooming works. Moving the view with the keyboard works too. Original bugreport: https://bugs.kde.org/show_bug.cgi?id=248986 I can confirm this behaviour here with QtWebKit from Qt mainline git (checked out 29th August). It does not work in rekonq, arora and Konqueror with WebKit KPart. Additionaly it does not work on Midori (GtkWebKit).
The website is the problem, not WebKit/QtWebKit. It is sending different resources depending on the user agent, and it is basing that on specific browser. Changing the user agent to Chrome or Safari makes the site work. Please report the problem to the website authors.