Basu Chatterjee's Khatta Mettha and F.C.Mehra's Hamare Tumhare both films were inspired by a foreign MGM Banner movie (Yours, mine and ours, 1968 starring Lucil Ball of The Lucy Show fame, the film was remade in Hollywood in 2005 with the same name) and both the filmakers saw the movie at the Festval and they decided to make it into a hindi film. Both filmakers dint know that the story of their films is same, later they got to know about it. Khatta Meetha was released first.
Umesh Mehra saw the film at a film festival and decided to remake it. But he heard Yash Chopra was planning to remake the film with Rishi Kapoor . Umesh Mehra decided to put his plans away. Then by chance he heard that Yash had opted not to make the film and was not making Silsila. Umesh decided to go ahead with his plans. But mid way thru he discovered Basu Chatterjee making Khatta Meeta, which was also a remake of the same film. Umesh spoke to the producers of Khatta Meetha and they didn't want to shelve their film. Umesh decided to work non stop and try to release his film before Khatta Meetha. But Sanjeev Kumar had a heart attack causing the film to get delayed. Then Rakhee Gulzar got ill and the film further was pushed back. Meanwhile Khatta Meetha released and did average business. When Humare Tumhare released it ended up flopping due to Khatta Meetha releasing first.