Hi there! Can you tell us step by step what you're doing to rotate the reference image? Using 2.5.15 here on XP Pro I'm currently able to rotate my reference images by bringing the cursor up to near the corner until it changes into the little circular arrow then left clicking and dragging to rotate. Perhaps we are doing something different though, do let me know and I can check it out for you here.
To increase and decrease the tool size, we use the right arrow key for 1% larger, left for 1% smaller or shift+right for 10% larger, shift + left for 10% smaller. Hope that's of some help!