Perhaps the 84 second burn overflowed the integer (2^6) and was caught by a 2^7s check (127s)
Mistakes happen. For example, may I introduce you to NASA’s 125 million dollar Mars Climate Orbiter, which spent most of a year traveling to the Red Planet before ignominiously burning up because a Lockheed Martin programmer decided to write the thruster-firing calculations in Imperial units (feet and pounds) instead of following the specifications to use metric units (meters and kilograms).