After running your snippet of code and piping it through cat -v, I get:

1234567.89
1.234.567.^H,89
1.234.567.^H,89
1234567^H.89
[download]

It looks like you have a remnant of a word boundry in your regex in that long statement, but because it's in the replacement side of the substitution, it's being treated as a backspace. Perhaps you meant it to go in the search portion of the substitution section?

Hope this helped,
-v.