Job mastery bonuses not stacking/applying

I've Assigned multiple dupes to learn gofer/courier then groundskeeper/plumber to get the strength bonuses, according to the job training descriptions I should be getting a permanent +8 to strength on every dupe who has mastered all 4 jobs. Selecting the dupe and looking at their resume it will show all the jobs mastered and +2 strength from all 4 jobs yet when you switch to their skills screen on all of the dupes I have tried this with, they only get the strength bonus from gofer/courier. I always started with gofer->courier->groundskeeper->plumber. Don't know if it will happen if I start with groundskeeper/plumber first.