News on this issue: according to my tests, the ModelClip scope ONLY malfunctions
in VERY specific cases when transparency is used on multiple Shape3Ds (BLENDED,
FASTEST, NICEST), and the bug can be qualified thusly:
When 2 or more transparent Shapes are rendered – and when they subject to the
influencing bounds and clipping planes – the Shape whose geometric Z is higher
(+Z) ends up "selected", and its scope will effectively become global to the
detriment of other ModelClip scopes that might apply.
As soon as one object's transparency is removed, Java3D behavior is as expected
and all scopes apply correctly.
I might add that even unscoped ModelClips exhibit similar, unexpected results
when transparency is used.
I'll wait for feedback before going further on this one. It will probably
require complex handing of Z depth during the actual render phase.