the condition to jump to the marker is “parameter is between 0 and 0.99”. If it starts off at 0, it will trigger immediately. This is why it is set to 1.0 to start with.
The AHDSR multiplies that parameter value with the envelope. It is param * 1.0 during the AHDS stage, and when stop is call, it has a downward slope which makes the release go from 1 to 0 quickly. ie when that ADSR hits .99 or .9 or .8 or whatever, now the parameter will be .99 or .9 or .8 or whatever it happens to hit, making the transition region condition trigger, and it will jump to the marker.