This issue is two years later still unsolved even with latest drivers:
Re: glVertexAttrib?f ignored on AMD?
Will this be fixed finally?
Renderer: AMD Radeon HD 6800 Series
Vendor: ATI Technologies Inc.
Memory: 1024 MB
Version: 4.4.13283 Core Profile Forward-Compatible Context 14.501.1003.0
Shading language version: 4.40