There shouldn't be a bug, unless it's a known issue with an older BIOS version on your motherboard, and you haven't bothered to update it. Even then, I doubt there would be a bug whereby you can't overclock them both together. It's probably a memory compatibility issue, as Ryzen's very fussy about the RAM type. Hopefully A.G.E.S.A. v1.0.0.7 will fix it. Motherboard manufacturers don't have access to the A.G.E.S.A. source code, only AMD, yet it is one of the most important factors in stability and memory compatability. Keep that BIOS on the latest beta version.