Serial Monitor must be open for Arduino <> Processing

I’ve been working on a project where I have a Processing sketch talking to Arduino via serial. I’ve confirmed that it works; the .pde creates the right packets, the arduino interprets the packets correctly, the wiring is all suitable and whatnot.

However, come runtime, the only way the system works is if I: First, open the Arduino IDE, select the correct serial port, and open the serial monitor. Second, run the processing sketch. (It doesn’t matter whether it’s been exported or if running from the Processing IDE) I can’t for the life of me figure out why this is. Any explanation would be nice, although I would prefer a suggestion for a fix; an automatic deployment is required.

Code is available: primarily in the gamepad_v3/gamepad_v3.pde and motor_v3/motor_v3.ino
Using Ubuntu & Processing 2.2.1
TLDR: Need Serial Monitor open for Processing <> Arduino and it simply boggles the mind