Yeah it's a bug in the software from the forum providers, they know and assume will release the fix when they have it.
You know that hosting a website and all its images costs money right? Predecimal is 100% free and all paid for by Chris, many of the other sites have subscribers or donations to help run the site, whereas this place doesn't. The 500kb limit is actually plenty as well, I've never had a problem myself and everyone else seems to manage ok. The method of selecting images, to me at least, is pretty straightforward? Bar the bug you came across, it literally takes 3 clicks add an image.
If it helps I can show you a couple of ways to reduce the size of an image, you'll find that you can get everything you need within the 500kb limit, especially in the case of photographing coins.