I've posted the same question in the support community but probably this is a better place for this problem.
So here is the short description:
After changing the window style (from border+caption - aka windowed - to popup - aka borderless) the OpenGL (3.1) device is not updated correctly. When the client area of the window is changed (so the context is "resized"), everything works fine.
This problem cannot be reproduced with any other AMD or NVidia card (at least where I could test it).
A source code with a more detailed description, a compiled binary and some images can be found in the attachment.