Energy saver: do the battery settings apply during charging?
This sounds like a bug in the power management software and I cannot reproduce the issue with my current MacBook Air.

Have you been watching the power settings with the pmset command?

The -g log command might show you something to help debug why this is happening. Worst case, you can have a few tabs open in terminal and watch -g pslog and -g assertionslog to see if some program is somehow overriding the defaults that you have set.

These logs and the timings would also make for a good bug report if you determined that it was simply an error in programming on Apple's part.