If you read the old version you can see Walter have Two personalities (Therefore Bipolar). As you can see in the video (i'll put link) there's one time event on Lars on day 8. When Talbot cutscenes appear, Walter will being weird and talk to himself such as "Tch, that's so annoying.", when you replay the cutscenes Walter will being normal such as "I'll get going now, take care".Click this video for information