linux - udev rules doesn't work with small number

I was writing a udev rule that makes use of the ID_PATH, just to make the device persistent against the port it's inserted in.

So here is what I have

  KERNEL=="ttyUSB?",SUBSYSTEM=="tty",ENV{ID_BUS}=="usb",ENV{ID_PATH}=="pci-0000:00:12.0-usb-0:1:1.0",SYMLINK="bla"

Initially, the file is called 52-foo.rules, and it doesn't work. I renamed it to 81-foo.rules and it works fine.

It's like the ENV{} values are only valid if the number are large enough. Could somebody explain why this is the case?

Thanks,