\bar ":|:" inconsistency?

[Steve Shorter]

Howdy!

        I was wondering about the apparent difference in repeat bars

        Seems

\bar "|:"


        and 

\bar ":|" 

        et al have a thick bar, followed by a thin bar followed by the ":"

        but

\bar ":|:"

        only has the thick bar followed by the ":". 

        Checking other printed scores shows that the convention is
to always have a thin bar just before the ":". 

        See

        http://linuxsweet.com/bar.pdf

        for a simple example.

        Is this a design decision, oversite or ???

        thanx - steve