Dimensions on Model and Paper space

I'm starting studying AutoCAD 2006 and learned that dimensions may be
drawn both in model and in paper space.
So I draw a square in model space with 4 points A,B,C,D. All sides are
100 units long. Then I draw a dimension from A to B: of course it shows 100.
Then I enter in paper space setting the scale=.5XP and start drawing
following dimensions :
From C to D: dimension =100
From D to A: dimension =100
From B to C: dimension =50 (!)
From C to B: dimension =100 (!!!)
From A to B: dimension =50 (!)
From A to D: dimension =50 (!)
It seems that when I start drawing a dimension line from a point where
already exists a dimension drawn in model space I get a wrong measurement.
I looked everywhere on my books and in the Help files but couldn't find
any explanation of this result.
Is this a feature or a bug?
Horst

 

At first I thought this was a simple case of someone not knowing about
paper/model space (always draw full scale, dimension in paper, etc.),
however I had to try it.

I think what you've done is actually dimension from the other linear
dimension's grip points and not the end points of the line segments.
Change your snap settings and turn off nodes snap temporarily.