bubbler redux

[sagehen]

Jas. Bamfort in /A Pretext for War/ quotes a CIA case officer referring to
some staff members in a particular situation as "bubblers." From the
context I can't be sure this isn't just a nonce usage to suggest idling at
idiotic level, but maybe it has another slang meaning......? I remember its
being discussed here in connection with drinking fountains some time ago,
but don't remember if other definitions came up then.
A. Murie