Shelby is like Arnold in Commando, killing everyone without even reloading. Watch the movie and see if he ever reloads.
Luckily, Mrs OldBag, I mean Sheppard, didn't seem too bothered by Stalin! leaving to get the flowers. And i'd say that saving the pitiful yet cute Lauren was a special case in terms of fuck-ups. Plus the game didn't make it very clear.
Sadly Stalin didn't notice the flowers as he was walking in the corridor, perhaps after a while... you can do a perfect playthrough of this game :)
PLEASE stalin I BEG you not to reload any part in the future it'll took away all the suspense if we already know you'll redo every part you fucked up