Why is "shared" attribute set on a folder?

While recently playing with a file synchronization utility on a
10.4.2 box, I noticed that there were some folders on one of the
two computers where the "shared" attribute had been enabled. In
all the research I've done, I've seen that this attribute is only
meaningful on files, NOT folders. Indeed, Apple's own documentation
(http://developer.apple.com/technotes/tn/tn1150.html) says that the
underlying structure flag is only for plain files:

kIsShared = 0x0040, /* Files only (Applications only) If */
/* clear, the application needs */
/* to write to its resource fork, */
/* and therefore cannot be shared */
/* on a server */

I can't think of any reason why this might be set on a folder, other than
an erroneous application having done so at some point in the past. There's
no discernible pattern to which folders were having it attribute set, and
which remained with the attribute cleared (i.e. application packages that
are presented as single files to a user in the Finder).

Does "kIsShared" serve ANY purpose on folder? Or is it harmless to run
around and turn them all off with "SetFile -a m dirname" ?

(FWIW, the program that exposed this oddity will see files as "different"
if the HFS attribute flags don't match. It's obvious that some bits should
be masked off from the comparison for folders, since they are meaningless
to examine. I'll be reporting this as a bug to its author.)