OK. I think I have figured out what's going on. The newer versions are MUCH more picky about attach being selected. Here's what happens.
In v2018: Draw a simple box with walls; say 10' deep x 20' wide. Auto dimension and set as necessary. Now block move the left 10' wall (doesn't matter which really) over 2' so that you will have a new width of 18'. Do this with "attach" NOT selected which will leave the front and back walls still sitting at the 20' mark. Then use adjust command to shorten the 20' wall so that it will cleanup and make the new corner at 18'. Cleanup again if desired. Dimensions will jump all over the place and reference the air space, center of brick, 1.15 inches into the stud, Jupiter, etc which forces you to redo those dimensions. However it seems to behave like the old way if "attach" is selected.
In the older versions, v13 in my case, you can do this same thing with attach selected OR NOT and it will cleanup the adjusted walls at the new corner and the dimensions/extensions jump back to exterior stud face as they should. In the newer versions, v2018 for me, you MUST have attach selected before the block move and it seems to cleanup properly. Otherwise you get the extensions referencing whatever they choose, even open space.
While this may not be a big problem for some, after years of use with the older versions behaving much better in this regard, I now feel that I have to constantly watch dimensions, add them up, zoom in to see where they are referencing, etc to be sure I didn't forget to check "attach" at some point and send out faulty dimensions. This needs to be fixed. The older versions didn't care if you select "attach" or not. It would always snap back to reference where it should instead of out in the "yard" someplace. At least for me it does. I never had to worry about it before.
Sometimes I wish I would have stayed in the older atmosphere.
Thanks for reading.
John