Just so I understand, you’re saying you did not already know how to make the bar and when you rescued a barkeep it didn’t have an option to teach you? If that’s the case then, yeah, that’s definitely a bug as you’re supposed to be able to learn it either way.

From my understanding and experience, if you learn it through knowledge points then the option to learn from a rescued barkeep doesn’t show up on the conversation list when talking to them as you already know it. And obviously, if you learn it from a rescued barkeep first then you can’t use points to buy it as you already know it.