How to make Modem Manager ignore non-modem USB serial devices?

[Paul Stoffregen <paul pjrc com>]

What is the current recommended way to request the Modem Manager ignore 
a USB serial device which is not a modem?

Until recently, this udev rule worked.

KERNEL=="ttyACM*", ATTRS{idVendor}=="16c0", 
ATTRS{idProduct}=="04[789]?", MODE:="0666", ENV{ID_MM_DEVICE_IGNORE}="1"

I've had at least 3 users report problems which appear to be related to 
newer versions of the Modem Manager apparently no longer respecting 
ENV{ID_MM_DEVICE_IGNORE} and opening the device shortly after it enumerates.