Can someone please verify something for me before I take it to my VAR?  I have "Enable on screen numeric input on entity creation" and "Create dimension only when value is entered" selected at Tools > Options > System Options > Sketch.  When I use the new Midpoint Line function with SW2015 a dimension box will pop up, as shown below.  I enter the desired value on my keyboard and hit Enter.  The line is there, and at the right length, but the dimension disappears and the endpoints aren't constrained.