The power meters on the StagesBike must communicate with each other in order to provide proper data to the StagesBike and connected apps. Some users want to disconnect one leg and pedal only with the other for single leg drills which can cause strange behavior. The power meters use ANT to communicate so they actually dont know anything about each other, which means that they make assumptions about the other. For example, if the left power meter is out of battery, the right meter waits 45 seconds of not hearing anything from the left meter and then assumes the left meter is dead, and it begins to function as a right only meter, doubling right power. The rule here is:

15 seconds before you get left only power, 45 seconds for right

Given this, the best way to do 1 legged drills is to leave the other leg attached to the pedal, but only concentrate on pushing with one leg. This will prevent the power meters from assuming its partner power meter has run out of battery.