Yes, get the shield at 100%, just charged it from 77% and it did stop at 80.Is the shield appearing next to the battery icon before you're unplugging the phone? If not you need to keep charging the phone until it does. After it appears it should go back to charging to 80% next time.
Then plugged it back in 20 minutes later and it went past 80 again. Quick Google suggests a few are seeing odd behaviour since about September.