It's because a lot of this is cutting edge and constantly changing from new developements/advancements. Features come and go as they get depracted and improved upon etc. I'm pretty sure custom headers WERE working a few months ago because I saw them awhile ago, at least I think I remember seeing them, but yeah, as of today, I don't see them. I think these issues will be ironed out soon, personally. I'm sure they're grinding on their end because I know I am on mine, lol.