(UK mobile network) giffgaff.com does this.
You can enter any length (as far as I can tell) on the "set password" form but the login form will only submit 25 chars.
This means you can successfully set your password to something you can never enter!
I've run into this kind of issue before. I had an 11-character password silently truncated to 10 on signup, then when I typed the full one into the login form it failed to log in.
Woo. Can't remember what clue the system gave me that let me figure out what had happened now.
This means you can successfully set your password to something you can never enter!
It has been raised in their forum but the discussion there is drowned out by people missing the point entirely. https://community.giffgaff.com/t5/Help-Support/Password-Limi...