Your console sounds like its a 5550 IP Console. The reason they have to turn tones on, is the 5550 is a "hot dial" keypad. Meaning that if you dial any digits normally, it will attempt to transfer a caller to those digits. My turning tones on, it sends the DTMF over the conversation.
Normal Mitel phones don't need to have a tones on or off feature as their keypads aren't hot dial. Only consoles have the hot dial feature.