TL;DR
Preserve the "Products finished:" counter value when quick-replacing a furnace, assembling machine, and/or anything else that works like those things.What ?
When I go to quick-replace a furnace with a different level of furnace:Its "Products finished" counter (new in 0.15) gets "reset" to 0:
I propose that the replacement's "Products finished" counter should keep counting up from the previous value. This feels similar to how inserters seem to keep at least some of their metadata (logistic network connection, filter settings) when quick-replacing them.