The IEEE Spectrum Magazine is reporting that the Huygens probe would not have returned data to Cassini when released to probe Titans atmosphere.
None of the participants from the manufacturer through ESA to NASA realised this could happen, partly because the Italian manufacturer saw JPL as a rival and wanted NASA to sign an non-disclosure agreement to protect their proprietary design, which NASA refused.
Disaster was averted when Claudio Sollazzo, Huygens’s ground operations manager at the ESA became uneasy about this not being tested, and asked Boris Smeds (also of the ESA) to investigate. He finally persuaded NASA to relent and allow the test and demonstrated that Cassini would not understand the signals that Huygens sent because of the doppler shift as it accelerated away due to Titans gravity.