Hum, the bonus seems to apply, it is just not listed separatly :
1- you get 5 production per material at the start of the game (some techs and buildings increase this value)
2- you add +3 prod per material from the workshop
3- you add +3 prod per material from the lumber mill
Total is 11 production per material, corresponding to what is listed for this city.
Am I missing something ?