What is the reasoning for the offset when the pipe was drawn not matching up with the end elevation of the end point marks when using bottom and top justification?
The assumption here is that you had a "hard ceiling" or "hard deck" (to take some terms from a completely unrelated flight analogy) that you were trying to draw around. You set the justification to "top" and the offset to 10' and draw. When you change sizes, the "top" remains at 10'. When I actually try this in 2008, I seem to be getting some results that I wouldn't expect, so some of my explanations of what the "idea" was may not make sense with what is actually happening.
Why does the (pick bottom justified pipe) end marks show up at the bottom of the pipe but the elevation information still refer to the middle of the pipe and if you alter that elevation it reverts back to the middle justification?
OK, hold 2 questions confuses me. Let me try to answer them separately...
Why do the bottom justified pipe end marks show up at the bottom of the pipe but the elevation information still refer to the middle of the pipe?
So, I'm going to start this answer with a question (actually I started it with a statement, since I said I was starting with a question). Do you want the pipe to move when you change it's justification? If you have a pipe drawn right justified so that it is tight to the wall, but you don't want to use eccentric reducers, so you change it to center, do you want the location of the pipe to actually change? Our assumption was that you don't, you just want to adjust the justification. That's why we always report the "offset" of the pipe as the "center" of the pipe no matter where we draw the "justification controls". If we only track the "justification" point and you change that then we would need to move the pipe from its current location to align with its new justification point. If we track the center points and you change the justification then the justification can change without moving (and possibly disconnecting) the pipe.
if you alter that elevation it reverts back to the middle justification?
I'm actually not seeing that behavior, but I am seeing a defect in the elevation that the controls are reporting after the pipe offset is changed. I'm seeing the pipe still be justified as it was (justification is set correctly for the pipe, and the controls are correctly drawn at the top or bottom), but the control are reporting the "offset" rather than the control location (offset +/- 1/2 Pipe Diameter).
I was expecting the elevation information and the manual adjust of the pipe by changing the end elevation marks to match up with whichever justification was used.
I certainly understand this expectation, but one thing that you need to be aware of is that in many cases the onscreen controls actually don't report the "correct" number even when they are middle - center justified. If I have a pipe that is sloping and it connects to another sloping pipe through a 90º elbow. Let's say that the 1st pipe has a lowest middle center elevation of -3'0". If you select the other pipe you'll see that it reports its highest middle center elevation as -3'0" as well. Neither of these pipes actually have a middle center at -3'0" (and the properties dialog will confirm this), but the controls, in this case report the elevation of the "imaginary intersection" of the pipes, so that you have a chance at some day getting them to match up when you want to try an connect things. Otherwise you would have to try to take into account the amount of elevation change that the elbow between the two pipes makes, because it is also installed at a slope (kind of a "double" slope). We could never figure this out easily when we were trying to make connections between sloping pipes, so we decided to let the computer figure it out for us, and to simplify the onscreen interaction by reporting this "incorrect" (but much more calculable) number, rather than being strictly correct (but impossible to use).