Well, nobody's tried to answer this, so I'll venture a guess (I've never used nistbladm).

It sounds like the program is waiting for input. Some password-changing programs will open the controlling TTY (through /dev/tty) directly rather than reading stdin or using command-line args. Is that the case here? (Note that there may be a bug where it opens and tries to read /dev/tty even when it's not supposed to.)

HTH ... maybe a little