Raspberry Pi USB to serial - multiple ACM0 devices spawning

Question

I am trying to get a Raspberry Pi running Octoprint (a kind of 3D print server) to talk to my Lulzbot Kittaz (RAMBo controller board, an Arduino Mega derivative), but something keeps creating bogus serial ports that seem to be getting in the way.

Here's what I know:

I try and connect over USB and here is the error message I get in the octoprint console:

Error: SerialException: 'device reports readiness to read but returned no data (device disconnected or multiple access on port?)

Further googling has lead me to SSH in to the pi and run

dmesg | grep tty

and I get:

[    6.117809] cdc_acm 1-1.4:1.0: ttyACM0: USB ACM device
[   28.949094] cdc_acm 1-1.4:1.0: ttyACM0: USB ACM device
[   35.389154] cdc_acm 1-1.4:1.0: ttyACM0: USB ACM device
[   36.119582] cdc_acm 1-1.4:1.0: ttyACM0: USB ACM device
... on and on
[  146.219829] cdc_acm 1-1.4:1.0: ttyACM1: USB ACM device
[  156.209130] cdc_acm 1-1.4:1.0: ttyACM1: USB ACM device
[  166.450016] cdc_acm 1-1.4:1.0: ttyACM1: USB ACM device
[  167.590072] cdc_acm 1-1.4:1.0: ttyACM1: USB ACM device

If I reboot the pi, without the printer connected, the output is:

[    0.000000] Kernel command line: dma.dmachans=0x7f35 bcm2708_fb.fbwidth=720 bcm2708_fb.fbheight=480 bcm2708.boardrev=0x10 bcm2708.serial=0x6024d696 smsc95xx.macaddr=B8:27:EB:24:D6:96 bcm2708_fb.fbswap=1 bcm2708.disk_led_gpio=47 bcm2708.disk_led_active_low=0 sdhci-bcm2708.emmc_clock_freq=250000000 vc_mem.mem_base=0x1ec00000 vc_mem.mem_size=0x20000000  dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait
[    0.001437] console [tty1] enabled
[    0.646366] dev:f1: ttyAMA0 at MMIO 0x20201000 (irq = 83, base_baud = 0) is a PL011 rev3
[    1.033111] console [ttyAMA0] enabled

As soon as I connect the printer to the RasPi, ACM0 and sometimes ACM1 devices start spawning, with a new one appearing every 3-10 seconds. Which seems like that would be a problem for a USB to serial connection. I'm guessing this is the problem. Any ideas on what could be causing it?

Here's what I've done so far:

• Disabled getty
• Gotten the printer to work with another (lost) install of octopi in the same hardware
• Re-installed octopi 3 times
• Gotten the printer to connect to my Windows machine
• Re-uploaded the firmware to the printer