While fixing  bug 696345 , I requested a change to the OpenGL spec that changes how GL_TRANSFORM_FEEDBACK_BUFFER_BINDING behaves. It will no longer be modified when the glBindTransformFeedback is called. See the Khronos issue for rationale:

https://gitlab.khronos.org/opengl/API/issues/66

I have implemented this change in Chrome's command buffer and ANGLE. SwiftShader will also need to make this change.

Chrome change: https://chromium-review.googlesource.com/c/chromium/src/+/924825
ANGLE change: https://chromium-review.googlesource.com/c/angle/angle/+/853130