NAS SSH doesn't free command line

[Jean Eckard]

Hi!
I'm having this problem with my NAS running busybox 1.10.3 and
dropbear sshd 0.51 :
When I type "exit" at the end of my ssh session, I don't get control
back; I have to close or kill the terminal window. Same with rsync,
when backups finish I don't get the command line back, I must close
the terminal window (and then who can tell me my backup succeeded,
although the size seems to be OK?).
Thanks for your help!
Jean