OpenCL 2.0 relaxed limitation where global work group size must be multiple of local workgroup group size. AFAIK R9 270X does support 2.0 but 6520 does not.
Sadly no, R9 270X doesn't support OpenCL 2.0.
Thanks for reporting this. It seems that "not divisible work-groups" are running fine on GCN cards but not on pre GCN i.e. VLIW/TeraScale cards. As I checked on the following cards, my observation was as below:
HD 6520G --> failed
HD 6850 ---> failed
HD 7870 ----> worked
R9 290X ---> worked
So, though the relaxation is an OpenCL 2.0 feature, however, it seems that the feature is working fine on any GCN cards. I'll check with concerned team and file a report, if needed.