I remembered it as funny, but boy, when I re-watched it, I sure was wrong. But yes, the film DID set it up as a comedy, and in retrospect, I wouldn’t have classified it that way.
I don’t like that in a movie. Be a drama. Or be a comedy. But don’t be both.
The best example to me was a movie “Love & Other Drugs” with Anne Hathaway and Jake Glynenhall. They played drug representative (the kind who peddled their drugs to physicians) and my wife and I howled at the first half of the movie, we both thought it was brilliantly funny. We both spent our careers in medicine, and we had seen these kinds of people often enough in real life to make it hit our funny bone, from the slicked back hair and pointy shoes to to the rolling bags they carried their drugs in.
I thought it might have been one of the funniest movies I had seen in years.
And then they got serious.
In the second half of the movie, it got totally serious, and it completely ruined the movie.
As far as movies go, you may be more right than wrong about that, and sounds like you and the Mrs were greatly disappointed in a badly done shift of gears in Love & Other Drugs; but in some cases it depends on personal taste and the art of the filmmaker. Fellini, for example, was a master at sifting his childhood pain through his plots and making it hilarious, or tenderly touching, in hindsight — I'm thinking of Amarcord in particular.
IMHO, the TV series The Sopranos combined drama and comedy exceptionally well, although the funny stuff was sarcastic cracks and surreal setups rather than slapstick. But when the same writer, David Chase, created a Sopranos prequel movie, it was awful. There was plenty of “thug porn”, but little of the ludicrous humor that had undercut the vain pretentions of the mob in the TV version.
Then again, I'm a person who loves ludicrous humor, anywhere, any time—especially when it comes out of left field. I'm reminded of the Irish wit Oscar Wilde's reputed last words: “My wallpaper and I are fighting a duel to the death. One or other of us has got to go.”