I believe the space is put in when the textcode for the smilies
Code:
:laugh4:
meets up with the line length in the post editor. While the actual smilie gif doesn't take too much space, the code for it is 8 chars long. Repeated smilies with no spaces in between will get a spce inserted, just like a long string of uninterrupted letters, like so:

skjfgksdfkdfksdfkjdfhkdhfsdkfhskdjfhkdhfksdjfhkdfhkdjfhkjhfkjdfhksjhdfksdjfhksdhfksdjhfkshhkdfsk


Now back to our regularly scheduled program...