Width of the terminal window is 280 columns, and Debian prints text just fine.
However, psql output is totally messed up. When I type a command, it's not wrapped: if I exceed 80 symbols in a line, the rest is printed from the beginning of the line overlapping the first part (i. e. caret is returned). Same goes for printing query results: it tries to fits everything into 80 symbols per line, but at least doesn't overlap the text.
I've tried this command:
\pset columns 280, but it didn't help.
echo "$PS1" yields