Where should I report this?

You should report this here. What version of the mod are you using? We fixed an infinite exploit in version 4 of the mod.

Looks like 3.0.2

It's in a mod, I can disclose details, but it makes last stand enchantment OP, and anything that uses exp really easy.

I was directed to here to report the problem so I assume it's not the mod curators fault.

3.0.2 is extremely outdated. There have been many updates since then. I am not sure where you obtained the mod download from, however we are the mod curators and developers. The issue you are referring to has probably been patched. The exp issue I fixed was one where you could get an enchantment when you're at a low level, and then when you are at a high level the exp from disenchanting is worth more then when it was at the lower levels. Read this: #4

Yup, exactly what I was referring too. So the mod pack needs to update its mod version. I'll tell the mod pack owner. Thank you!

No problem.