What indication do you have that it is not switching? In the Energy Saver preferences, it always opens up showing the power adaptor settings. That doesn't mean the machine is using them. Look at the sentence at the bottom of the panel. For example, I'm on battery right now and it says, "You are using custom optimization. Estimated battery life: 2:43 remaining with current settings. Current battery charge is 85 percent." It's using my battery settings even though the "Settings for:" pop-up always starts at Power Adapter. Is this what you are talking about? The machine always switches. There just isn't a very clear indication other than this sentence.
Steve