I have had this same annoying problem many times. The only thing that seemed to fix it for me was setting the max and min image size to 0x0. I see you have that set so I don't know what to think. This issue needs to be resolved because it's very annoying when it happens. 10 years is flipping ridiculous.
Yep. I give up. I have looked at every setting between the 2 boards and they are exactly the same. They are mirror copies as far as I can tell. Using ANY url based image one will handle it just fine, one will not handle any image at all. Same server and what seems like exactly the same environment for php..