Sucks!
I'm going to be painting tins as well...I damaged the paint on the tank when removing/replacing the liner...found a scratch or imperfection and peeled the paint right off.
I've also had fuel peel paint, especially on a bike with a lot of lean on the kickstand. Had it happen on a hot day. Rode and then got fuel before a lunch break. Bike was in direct sunlight while I was in getting some wings and a beer (only one so it wasn't long) and fuel was running down the side when I came out. I thought I caught it early enough to avoid damage but the next morning went out to the garage and paint was peeling.