I'm just wanting to dimension something symmetric to a centerline, like this blue dimension below:

And that was successful in the instance above:  The symetry line is the dashed line, and I wanted to create the .750 offset line based on a 1.500 total distance.

The problem is, if the line to the left (that I am dimensioning) is a construction line, this type of dimensioning will no longer function.

This dimensioning scheme does not work for construction lines?  Seems like it worked in prior versions.

[Hurry, because it will snap to the midpoint.  And then  you have to redo the selection.  Above all, this should be what you are thinking about every time you are dealing with sketch entiies.]