Do not conflate the 'dmesg-warn' and 'warn' statuses. 'warn' is set by the framework when the test passes, but there is unexpected output on stderr, or sometimes by the test itself.

In this case the test itself is setting the warn status. From tests/spec/ext_transform_feedback/tessalation.c:

Note: some OpenGL implementations do not pass the "flat_first" and                                                                                                                                                                                                      
"flat_last" tests when rendering quads or polygons.  That is, they                                                                                                                                                                                                      
produce a tessellation which contains the correct vertices, but not                                                                                                                                                                                                     
in the order required to preserve flat shaded colors.  This is                                                                                                                                                                                                          
unlikely to cause problems for client programs, since client                                                                                                                                                                                                            
programs that use new features like transform feedback are unlikely                                                                                                                                                                                                     
to also use deprecated features like quads and polygons.  Also, it                                                                                                                                                                                                      
is a matter of interpretation whether these tests are expected to                                                                                                                                                                                                       
pass at all--after all, the spec does say that "the order of                                                                                                                                                                                                            
tessellation within a primitive is undefined".  Accordingly, these                                                                                                                                                                                                      
failures, should they occur, are flagged as warnings rather than                                                                                                                                                                                                        
failures.