Comment # 1 on bug 89152 from Michel Dänzer

I'm hitting several other GL error conditions first:

Mesa: User error: GL_INVALID_VALUE in glSampleMaski(index)
Mesa: User error: GL_INVALID_ENUM in glFramebufferTextureLayer(target=0x1)
Mesa: User error: GL_INVALID_ENUM in glDrawElementsInstanced(mode=8ca8)
Mesa: User error: GL_INVALID_OPERATION in glFramebufferTexture
Mesa: User error: GL_INVALID_ENUM in glBindRenderbufferEXT(target)
glGetError = GL_INVALID_VALUE

Try running the app with a debugging build of Mesa in gdb and setting a
breakpoint on _mesa_error.