Demo desyncing caused by bouncing Lost Souls

In Vanilla Doom, Lost Souls were originally intended to bounce off floors and ceilings when they hit them, but due to a coding error, the bouncing test was performed after the Lost Souls' momentum was set to 0. Doom 95 and Final Doom fixed this bug, causing many Doom 2 v1.9 demos to go out of sync.

Source

 * http://prboom.sourceforge.net/mbf-bugs.html