Sorry I can't be of more assistance, other than all the debugging tips and trying to find the difference between cat+stty and Perl, I'm still out of ideas at the moment. It could possibly be related to whatever kernel driver or USB module this is - in the node I linked to, I mentioned that I discovered that I needed to set -echo for some of the adapters I was working with (specifically, an FTDI USB-COM485-PLUS4 module with a FT4232H chip). Unfortunately, the way I discovered this was with lots of experimenting and banging my head against the wall. I recall using cat+stty, minicom, and screen to talk to the virtual port until I figured out the issue with the -echo option. I can only suspect that the issue with the module you're working with might be similar, some combination of options needed to make it work. Good luck, and let us know if you have more questions or you do figure it out :-)