In message <49cb1f99de0617537f881a018dc4727b@4096.net> on APAS, an anonymous user was confused that Mixmaster wouldn't accept a filename containing a "@" character and "freeze". The program is in fact treating the filename as a recipient address (from the documentation, this is good) and waiting for data on stdin.
A simple workaround in this case is to redirect the file (mixmaster < filename) instead of passing a file name.
So this is not an implementation bug, but an interface bug. The user did not receive feedback when a recipient address from command line was added to the message.
What happened:
$ mixmaster -p foo@bar
Mixmaster 3.0b2
[blocking]
What the user expected (bad):
$ mixmaster -p foo@bar
Mixmaster 3.0b2
Chain: austria,bikikii,cyberiad,4096
$
What I think is better:
$ mixmaster [-v] -p foo@bar
Sending message to foo@bar.
Go ahead and type your message ... (à la GnuPG)
[blocking]