Can reset Leonardo via USB in OSX, failing in Ubuntu

This is a distillation of previously posted questions, mostly reflecting what I've learned over the last week or so about Leonardo and its bootloader...

Consider the following minimal python program connected to an ATmega32U4 based (Leonardo-like) system via USB:

#! /usr/bin/python

import sys
import serial

ser = serial.Serial(sys.argv[1], 1200)

When run on my OSX laptop (./ /dev/cu.usbmodem1411), it resets the Leonardo. When run under Ubuntu (./ /dev/ttyACM0), it fails to reset it.

I understand that this is more likely a question about device drivers under Ubuntu than about the Leonardo, but has anyone observed this mis-behavior before? Or have suggestions about what to look for?

My first guess would be a permissions issue on the /dev/ttyACM0 device. You could test this by running the script as root (or sudo). If this works the fix is to add you userid to the dialout group.

Update: I'm a bit abashed to admit, but the problem turned out to be nothing more complicated than a separate process grabbing ttyACM0, so the reset was failing. Rather than deleting this post out of embarrassment, I'm leaving it here in case someone else makes the same bone-headed mistake.