Why SUBTRACT acts like UNION?

Hello everyone.
Every time I subtract something, everything on one side of the object
I subtracted is unified, and also everything on the other. Let's see
if I can clarify that with a simple example.
I have two cubes and one very thin plate that goes thru them. When I
subtract that thin one, four objects are left. Two that were over the
thin one, and two that were under it. Those two above act like I used
union on them, also those two under.
More importantly their layers are changed to currently selected one. I
don't know why, sometimes separate works and sometimes doesn't. But
their layers are changed anyway.
Is this behavior controlled by some system variable?
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Copy (with basepoint) the plane and subtract from one cube, then paste and subtract it from the other. I'm sure someone has a routine for this (or maybe there is a variable), but that's the manual solution.
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I know that. I was wondering how to disable it, but it seems there is no way.
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I know this wont help you, and really isn't on point, but I feel this is a good thread to mention it.
The only time I model in acad now is when i absolutely have to. IE: drawing complex shapes with precision, building a simple model to check relationships of different parts of my buildings, etc. I stopped doing it mainly because after r12, the modelling "tools" became all but extinct. Nothing resembling parametrics, no real way to modify solid objects except by copying, slicing, subtracting, re-combining the chopped up pieces to get your "whole" object you were trying to create. Besides that, you really have to save all your little bits and pieces and "helpers" you make along the way so that if your part needs redesign, you dont have to basically start from scratch to re-create it.
AFAIK, the only real improvements from release to release in acad solid modelling has been the accuracy and stability of the ACIS core... but that doesnt really do me any good when I dont want to need to use solids, or when I dont want to model in autocad because it's so cumbersome.
With autocad being as powerful as it is, it just amazes me that there isn't as complete a set of solid modelling tools as there is 2D drafting tools.
If nothing at all changed in the next 3 releases of acad other than bug fixes and the development of the modelling and rendering tools / environment, I think that would be one of the greatest strides taken in improving autocad in the history of the software.
just my opinion, for what it's worth...
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Trey Monsour
Will not happen. Why would they add modeling tools when they have other products (Inventor and Architectural desktop) for that? AutoCAD was never meant to be a serious solid modeler and probably never will be. As to the ACIS engine, if they were serious about solid modeling, they would use a more recent version. AC 2002 used ACIS version 4 and I would bet 2004 uses the same. Version 13 is now available. The reason they stay with version 4 is that solid modeling is not a priority and it's cheap. When you sell $500.00 software for over $3000.00, you can't afford to put any money into it.
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