"[]" Keys does not work when in a ssh session

[Simone Cogno]

When I'm in a ssh session the keys alt + "[" (alt+5) and alt + "]" (alt+6) does not work. Do you know why?

Also if then a copy some text and I paste it I got this result:
"[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[<copied_text>"

Edit: Every alt + number combination does not work

OS: MAC OSX El Capitan
upterm version: 0.4.3