Yeah, that's more or less a bug. The reason for it is that outgoing requests from Workers pass through a lot of the same proxy logic as incoming requests. This made Workers a lot easier to build initially (six months from inception to beta!) but there are a lot of quirks as a result.

Outgoing requests from Workers destined for external servers (i.e. not other sites on Cloudflare) really have no reason to be buffered and thus no reason to impose these limits. We should fix that. I also suspect most Workers-based apps don't really need incoming buffering either.