Confusing behaviour, when using for vocabulary with multiple parents

Hi,

In a (hopefully not too) special case the behaviour of the taxonomy select widget is uncomfortable - not to say nearly impossible:

I have a vocabulary with two hierarchy levels (say "primary" and "secondary" level).
Terms in the secondary level have often multiple parents in the primary level. That looks like:

A -> C
A -> D
B -> C
B -> E

When selecting A -> C in the first, then it is impossible to change to B in the primary level. The selection allways "jumps back" to A -> C before even showing the secondary level unter B.
Even when selecting B -> C in the first, the selection jumps to A -> C spontanously.
What works:
A -> C then A -> D (D must not be child of B) then B -> E (E not child of A)

I have the feature "save lineage" disabled, because it doesn't make sense in my application. "Force deepest" is enabled and all nodes will only be assigned to those secondary level terms.

I tried to enable "save lineage" which keeps the widget working like it should.
But I don't want to save the lineage for any node.

When saving lineage there is another side effect in using the "Hierarchical Select in a block as a taxonomy filter" ( http://drupal.org/node/534986 ) although this can easily be patched by not redirecting to the first but the second or last value:
The user is redirected to A, when selecting A->C which is not wanted.

What I would suggest as a solution:
Lineage should be "saved" during usage of the widget instead of searching for the first possible lineage to the second/third/... level term.
The difference of lineage saving or not should then apply just before saving the node.

Unfortunately I have no idea how to apply that idea to your code. Thanks for any help!