Generally in Windows, Control-Backspace deletes the previous word. In Mirc it inserts a garbage control character, both in single and multiline input mode.
Sorry, I disagree. I use 6.14 and the problem occurs.
The real problem is not that the character appears but that control-backspace is supposed to delete the previous word (as it does in any other windows application), and this does not work in mIrc.
Not quite. For example, try Notepad - you'll see it generates a $chr(127) character on ctrl+bksp as well. Another few quick examples from this WinXP installation: the text edit field in Paint and the address selection field in Addressbook.