Which Games Share Glu Credits (Kindle)?

Jinjrax

On my Kindle Fire HD I was under the impression that GLU credits would be shared across games on that same device. However I own Samurai vs Zombies defense 2, Bigtime Gangsta, and Guns Bros, but none share the same credits. I have 16 on svzd2, 32 on BG, and 0 on GB. I want them all to share the same credits so any suggestions?