I've had the same issue, I read elsewhere on here from a moderator that they're aware of the issue and currently developing a new software update that should resolve this issue. Since my first 5.1.1 update, I was able to download and install another, but the issue still persists. So I'm just hoping that the newest update I've just installed wasn't the keyboard theme update in question. Hopefully, it won't take too much longer because, in all honesty, the light theme keyboard is driving me kray kray. Even if I try to switch to the dark keyboard theme (which is still ugly as sin when popped up against my purchased themes) my phone still reverts back to the light theme despite the system settings showing as having the dark theme or galaxy theme as the selected choice.
The clear cache on the keyboard as well as the phone and the reset keyboard settings option only fixed things for a few minutes. Same as when I restart the phone or reapply the theme.
