Are you on SVN or version release.
That was probably on SVN 11394 (a week ago ?).
Changing the build order from less expensive units first to more expensive units first reduced the number of wasted

(comparing what my predicted production on the previous turn was to what was actually used while building, including the

in partially built items).
This is a big issue when planning : as an example scenario, imagine you get surprise attacked, and you see that with your current production you should be able to build 3 units in the nearby city (and then merge them), so you order that... but then the next turn only 2 of them have been built !
Whether there's a mechanic that makes you waste

or not-
(But then why would faster game speeds be disadvantaged ?
And why is this different from

that you get when someone else built a world wonder you were working on ?
I guess other items could have a worse rate of conversion... in fact why wouldn't it be exactly the same as the % of your current

to

conversion item ?)
-

being wasted is something that should be shown to the player, rather than happening "silently"...