Conflict between Site Categories and MarketPress

When MarketPress and Site Categories are enabled (only), and you try to assign a subsite to a category in Network Admin -> Subsite WP Admin -> Settings -> Site Category, the following PHP Warning is thrown with every instance of the category selection element:

Warning: Missing argument 2 for MP_Shortcode_Builder::wp_dropdown_cats() in /home/juswri2/ on line 144

See screenshot:

No category can be selected and saved.