I have been working with SW2016 for a few weeks now and the dimension tool behavior has changed.

According to the help docs...

"The selection behavior when you add a dimension to a sketch has improved.

If you select an endpoint or sketch point and
then accidentally click in the graphics area, the first selected point
is retained so you can try again to select a second entity.

If you select an invalid entity to complete a
dimension, such as a spline, ellipse, or parabola, instead of an error
dialog box, a tooltip warns that a dimension cannot be created from the
currently selected items. Move the pointer to
dismiss the message. Again, your first selection is retained so you can
select a second entity."

I personally would like to go back to the legacy behavior that worked for the last 10+ years.... anyone found a way to disable this "productivity improvement" ... Is there a revert to legacy behavior button.... this is driving me crazy ??   It constantly wants to dimension what ever the last thing that was selected... I find it very annoying..... HELP !!