you mentioned "slight breeze". even this will affect the um planes pretty well. mine would "bobble" around flying into the wind, but flying with the wind it was smooth. i think when i would fly into the wind the plane would climb and i would push the stick to try and keep the plane level, thus i was causing the bobble.
i've flown the um t-28 in around 10mph winds and its a handful. fun once you get confident enough to do it, scary as all get out if your new to flying!!
congrats on the maiden flight!!!!