I originally reported this as a seaborn issue, but it turns out that it is the tight_layout property that causes the xaxis to get narrower, then reverse and eventually throw an error if the axis title is too long. See this example notebook for details using both matplotlib and seaborn.

As I mentioned on the seaborn page, I don't think this is especially important and it's easy for the user to adjust by shrinking or splitting the title. I was just confused initially when my plots changed direction on the axis and didn't immediately relate it to the title length. Maybe a warning message can pop up when the axis title is very long, saying that it might have unexpected effects on the plot appearance?