GLX explicitly allows the sharing of window state. For example, all OpenGL renderers bound to a double buffered window share the same notion of front and back buffer state. This means if one client calls glXSwapBuffers on a window bound to by other OpenGL renderers, the other renderers maintain the same view of which buffer is front and which is back.
One requirement of GLX that proves difficult to meet is the sharing and management of ancillary buffer contents for multiple renderers bound to the same window. Ancillary buffers are non-visible buffers used by rendering operations. Examples are stencil, depth, and accumulation buffers. Sharing ancillary buffers is straightforward if they are supported in hardware, but sharing of buffers implemented via software is more difficult to correctly support.