This is obviously an incomplete feature: The TODO shows that they intended to actually plumb through the "metered" bit from the upstream interface, but never implemented it.
And this is a default, I suspect you can override this, either in the individual applications, or by disabling the "hotspot" option in the buried menu.
Yeah, it's a bit annoying if it's your default way of getting to the internet, but it's at least not going to cost you a massive pile of money as it sync's everything before you have a chance to turn off all the syncing. This way you can at least turn the syncing on again later if you're ok with it.
[Edit: speling]