I have a USB modem that sometimes enumerates wrong and creates a false device in /dev. How do I remove that bogus device ? How do I force renumeration without rebooting ?

When the modem works correctly, it produces this:

 crw-rw---T 1 root dialout 166, 0 Oct 15 21:51 /dev/ttyACM0
 crw-rw---T 1 root dialout 166, 1 Oct 15 21:50 /dev/ttyACM1
 crw-rw---T 1 root dialout 166, 2 Oct 15 21:50 /dev/ttyACM2
 crw-rw---T 1 root dialout 166, 3 Oct 15 21:50 /dev/ttyACM3
 crw-rw---T 1 root dialout 166, 4 Oct 15 21:50 /dev/ttyACM4
 crw-rw---T 1 root dialout 166, 5 Oct 15 21:50 /dev/ttyACM5

When there's a problem, it produces this (note the curious first line):

 -rw-r--r-- 1 root root 8 Oct 31 17:17 /dev/ttyACM0
 crw-rw---T 1 root dialout 166, 1 Oct 31 16:18 /dev/ttyACM1
 crw-rw---T 1 root dialout 166, 2 Oct 31 16:18 /dev/ttyACM2
 crw-rw---T 1 root dialout 166, 3 Oct 31 17:17 /dev/ttyACM3
 crw-rw---T 1 root dialout 166, 4 Oct 31 16:18 /dev/ttyACM4
 crw-rw---T 1 root dialout 166, 5 Oct 31 16:18 /dev/ttyACM5
 crw-rw---T 1 root dialout 166, 6 Oct 31 16:18 /dev/ttyACM6

How do I fix this ?