I'm doing the shake and stir quest- you're supposed to make and drink 5 creamy martinis. I made 5, they all counted towards the quest. I already had one creamy martini in my inventory before starting the quest. I drank all 6 martinis that were in my inventory, but only two counted towards the quest.
I forgot to add- I tried to drink all of the martinis at once. It's possible that the drinking limit kicked in and caused this bug- it only let me drink one or two on the first go.