Switching from OpenGL to GDI

What happened to you is, that up until now you relied on undefined behaviour – actually it never was supposed to work in the first place, and you were just lucky. Once you've set a doublebuffered pixelformat on a window that does not set the PFD_SUPPORT_GDI flag, you no longer can use it for GDI operations.

The OpenGL rendering context does not matter! A lot of people – it behooves me for what reason those who believe it do believe it – suffer from the misconception, that OpenGL render contexts in some way were tied to a particular HDC or HWND. Nothing could be further from the truth. As long as a drawables pixelformat is compatible to a given OpenGL context, that context can be bound to it.

And because there're no ties between your OpenGL render contexts and the windows, all that little dance of destroying and re-creating the context has no meaningful effect whatsoever. Maybe, just maybe, that little dance triggered some codepath in the driver, which made your illegal actions somehow work. But what's more likely is, that you just did the raindance in expectation for it to do something useful, while it was completely bogus in the first place, and you could just have not done it in the first place, to the same effect.

Are we doing something wrong,

Yes, yes you are. You are doing something, that never was allowed or supposed to work in the first place. You just didn't notice it, because so far OSs/drivers didn't make use of the wiggle room afforded to them by this not being allowed for you. However recent developments in GPU/OS/drivers now do make use of the wiggle room, and just steamroll over your code.

It is not an option to draw 2d content in OpenGL .

Why?

It is not an option to draw 2d content in OpenGL or vice versa. Also, the application is very performance sensitive, such that it is not an option to draw 2d content to an offscreen GDI image in order to draw it as an OpenGL quad

Did you actually try and profile it? 10 bucks says this would perform just fine.

A bit of search at OpenGL on Windows - Generic Implementation and Hardware Implementations reveals:

OpenGL and GDI graphics cannot be mixed in a double-buffered window.

An application can directly draw both OpenGL graphics and GDI graphics into a single-buffered window, but not into a double-buffered window.

And also from PIXELFORMATDESCRIPTOR structure

PFD_SUPPORT_GDI: The buffer supports GDI drawing. This flag and PFD_DOUBLEBUFFER are mutually exclusive in the current generic implementation.

Since you are using OpenGL 1.1, just add PFD_SUPPORT_GDI flag to your PIXELFORMATDESCRIPTOR pfd

I would not destroy the GL context. Instead I would try to change the

glViewport(x0,y0,xs,ys);

to small area in some corner or even hidden like

glViewport(0,0,1,1);

That way even if bug persist the user will see only pixel artifact in corner somwhere most likely not even notice it (especially if rendered with the same color as background).