Is the movement made by the worshipper, after hearing the imam's takbir to rise from bowing, and before the imam straightens up, then returning to bowing again, considered a violation that invalidates the prayer?

What you have mentioned is not considered an addition to the prayer, nor does it affect its validity, because you remained in bowing until the Imam rose. This slight movement does not cause harm, and we warn you against obsessive thoughts and giving in to them.