It appears that Drunkard's Regret properly prevents hangover from alcohol as of 1.2 (I recently resolved a bug I filed in 1.1 for this).
However, it does not prevent "Unforgettable Hangover" from drinking "Forgetful Night". I'm guessing Drunkard's Regret was updated to properly prevent the "hangover" effect from most alcohol, but this left out the special "unforgettable hangover" effect from Forgetful Night.
Here's a dropbox link to an autosave where someone has the drunkard's regret equipped and a forgetful night buff, along with an output_log from a game in which the unforgettable hangover effect occured nonetheless. To reproduce this issue, simply rest and consume any food other than mariner's breakfast (which prevents any hangover). https://www.dropbox....uFZ3QUNBta?dl=0