Khronos public bugtracker – Bug 318
Stencil1,Stencil4 and Stencil8 tests do not set the viewport for rendering to the texture
Last modified: 2013-06-06 02:43:48 PDT
The texture being rendered to is 512x512, but there is no change to the viewport to accomodate this. Therefore when the screen size is smaller than the texture only part of the texture is being rendered to. This is in the tests defined by the source GL2ExtensionTests/GTFExtensionTestStencil8.c etc.
This is fixed by adding
glViewport(0, 0, 512, 512);
at line 317 (after glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);)
glViewport(0, 0, windowWidth, windowHeight);
at line 323 (after glBindFramebuffer(GL_FRAMEBUFFER, 0);)
In the similar GL2Tests/GTFGL2TestFramebufferObjects.c source code the viewport changing does appear to happen.
If this is still an issue, please raise it through internal Khronos