job control doesn't work when I try to set up getty over serial

I am trying to set up getty to log in over serial (mainly as an experiment). With almost any configuration, the same thing happens. If my default shell is bash, I get this message after I log in:

-bash: cannot set terminal process group (15297): Inappropriate ioctl for device
-bash: no job control in this shell

and then to prove that it doesn't work, I can't use ctrl+C to stop programs:

$ sleep 30
^C

and it doesn't seem to send the signal. These are the configurations I have tried: I have tried both of these commands

# copied from raspberry pi:
sudo /sbin/agetty --keep-baud 115200,38400,9600 ttyUSB0 vt220
# something else I read somewhere
sudo getty -L ttyUSB0 9600 vt100
# (I know I'm mixing and matching a lot of differences but the result is the same)

I have tried both screen and picocom as a client. I have tried using a rasberry pi as a server, and two different ubuntu laptops. I have tried two FTDIs, two RS-485 usb adapters, and a built in RS232 on the getty side with a USB RS232 on the client side. I have also tried changing my default shell to sh and dash. I don't get the message, but ctrl+C still doesn't work as expected The funny thing is - when raspberry pi's automatically configure /dev/ttyAMA0, and it uses exactly the getty command that I have put, job control works! And the terminal settings are almost identical. (except for -iutf8 actually) here are the terminal settings with the FTDI connection, and picocom running:

$ stty -a -F /dev/ttyUSB0
speed 9600 baud; rows 24; columns 80; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D;
eol = ; eol2 = ; swtch = ; start = ^Q;
stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W;
lnext = ; discard = ; min = 1; time = 0;
-parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal
-crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr
-icrnl ixon ixoff -iuclc -ixany -imaxbel -iutf8
opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0 cr0
tab0 bs0 vt0 ff0
isig -icanon -iexten -echo echoe echok -echonl -noflsh -xcase
-tostop -echoprt echoctl echoke -flusho -extproc
$ stty -a -F /dev/ttyUSB1
speed 9600 baud; rows 0; columns 0; line = 0;
intr = ^C; quit = ^\; erase = ^?; kill = ^U; eof = ^D;
eol = ; eol2 = ; swtch = ; start = ^Q;
stop = ^S; susp = ^Z; rprnt = ^R; werase = ^W; lnext = ^V;
discard = ^O; min = 1; time = 0;
-parenb -parodd -cmspar cs8 hupcl -cstopb cread clocal
-crtscts
-ignbrk -brkint -ignpar -parmrk -inpck -istrip -inlcr -igncr
-icrnl -ixon -ixoff -iuclc -ixany -imaxbel -iutf8
-opost -olcuc -ocrnl onlcr -onocr -onlret -ofill -ofdel nl0
cr0 tab0 bs0 vt0 ff0
-isig -icanon -iexten -echo echoe echok -echonl -noflsh -xcase
-tostop -echoprt echoctl echoke -flusho -extproc

What am I doing wrong? And why does it work with the built in configuration for the built in serial port on the raspberry pi?