Steps:

1. Upload an image to a design category, order it, and save.
2. Select another design category, add design, and select that former image we selected in the first step, order it, and save

Results:

• Both images will be ordered to the last design category you saved.
• If you rearrange the image in step 1 it will completely remove the design from step 2. 
  

Thanks for bringing this up! I'll let the developer know.