OSX: tty.usbmodem exists, but only cu.usbmodem appears in the serial ports menu

I'm having issues connecting to my ATMega16u2 uno: in the Port menu, the CU ports show up fine, but none of the TTY ports are listed. I can send to the CU port, but the sketches I want to run have bi-directional communication and it is not working properly - if I upload a program to my Uno with Serial.println, it wont let me upload anything without disconnecting and reconnecting the USB:

avrdude: stk500_getsync() attempt 1 of 10: not in sync: resp=0x00
avrdude: stk500_recv(): programmer is not responding

The TTY ports definitely exist on the computer:

andy:dev Andrew$ ls -al /dev/tty.*
crw-rw-rw- 1 root wheel 17, 2 Jul 12 09:41 /dev/tty.pci-serial22
crw-rw-rw- 1 root wheel 17, 0 Jul 12 09:41 /dev/tty.serial1
crw-rw-rw- 1 root wheel 17, 10 Jul 12 10:00 /dev/tty.usbmodem14a31
andy:dev Andrew$ ls -al /dev/cu.*
crw-rw-rw- 1 root wheel 17, 3 Jul 12 09:41 /dev/cu.pci-serial22
crw-rw-rw- 1 root wheel 17, 1 Jul 12 09:41 /dev/cu.serial1
crw-rw-rw- 1 root wheel 17, 13 Jul 12 10:11 /dev/cu.usbmodem14a31

I have tried switching USB cables, switching USB ports, and switching computers. On my laptop (also 10.10), the TTY ports still do not show up, but the CU port is less of an issue since I can run and re-upload programs that use Serial.println. Maybe there is something on my main computer that is stealing the CU connection as soon as it writes so that the uploader cant upload new sketches; I dont know how to check for that. From what I understand, the reason that the TTY ports exist is to enable bi-directional communication without locking it up.

Is there some way to enable the TTY ports on OSX that I missed?

asmiller:
I'm having issues connecting to my ATMega16u2 uno: in the Port menu, the CU ports show up fine, but none of the TTY ports are listed.

The port list (now) filters out tty devices.

asmiller:
I can send to the CU port, but the sketches I want to run have bi-directional communication and it is not working properly

That has nothing to do with if you selected the tty or cu devices.

If you still think it matters, just roll back the IDE 1 or 2 releases.