Every time I donate food to Charity, I end up giving her two items with one click. I still seem to get prizes regardless but this is still a problem, especially if others don't plan on giving her all/more than one of a particular item. I use chrome, no I haven't cleared my cache (and won't,) and no I haven't tried this in firefox yet but I assure you, my problems usually never suffer from those kinds problems. I did run into trouble during the plot due to some of my personalized subeta code so that might be an unforeseen cause to my problems if anyone wants to check.
I'm getting the same thing with the bonfire, running Safari on macOS Mojave. However, I am getting the right amount of items back. For example, I'll have 6 of Blue Fiery Red Rreign Beanbag and click once to throw one in. After that, I'll have 4 Blue Fiery Red Rreign Beanbag but two event item rewards (wreathed/minions/etc). If I only have one of the item I'm throwing in, it works as expected.
Can't say I mind the error tbh but it's probably not supposed to work that way