These are one set of steps to be effected by the bug.
1. Have a primary hardrive that is nearly full.
2. Get a second hard drive to store more pictures to your machine.
3. Change My pictures folder location to save on the new hard drive. (The least likely step but not super unlikely if your searching ways to stop your primary hard drive filling up)
4. Click no when asked if you want to copy everything across to the new location (ignoring it saying it's recommended (but only so you can see your older photos easier))
5. Have the update roll out and delete all of the old photos you had.
Losing those old photos (perhaps of passed loved ones) you may not have anywhere else can be heartbreaking. The fact that a very small percentage of users is effected does not change the fact that as we're talking about a massive user base, the absolute number of users is always going to be high.