You're logged in to a remote host via ssh, about to su or whatever and just as you begin typing your super secure, character set conscious password you get:
Password: ~v [LogLevel DEBUG]
su: Authentication failed
You have just tripped an SSH escape sequence. From man ssh:
ESCAPE CHARACTERS When a pseudo-terminal has been requested, ssh supports a number of functions through the use of an escape character. A single tilde character can be sent as ~~ or by following the tilde by a character other than those described below. The escape character must always follow a newline to be interpreted as special. The escape character can be changed in configuration files using the EscapeChar configuration directive or on the command line by the -e option. The supported escapes (assuming the default â€˜~â€™) are: ... ~V Decrease the verbosity (LogLevel) when errors are being written to stderr. ~v Increase the verbosity (LogLevel) when errors are being written to stderr.
The solution is simple: either choose a password that doesn't begin with an escape sequence or enter a double tilde: ~~