Go to Figure and deselect the Inverse Kinetics for both legs (for some strange reason they have it defaulted to being "on").

However, if you want your figure to sit, it is usually better to have the settings checked "on", select hip to place the figure into position, and then uncheck the Inverse Kinetics for the rest of your pose. Someone told me that and it was very helpful, and I wish I could remember who so I could thank them properlyu.