it could just as well be my imagination because I always do this stuff late at night but all I know is empty space = double logon. Remove empty space and single logon, single logout.
This probably only applies to wordpress (not wpmu) because it doesn’t create these keys and when you paste it(just the key) into bbpress config the spaces are removed so you are left with a cut and paste job in wp-config of a space that will not match.