Steve, we have found a work around for this.
Start a sketch,
Draw a line
When Modify box shows up, click the "reset spin increment button" 2nd from right
Type in 0
Click on "reset spin increment button" again
select the newly added 0 and check "Make default"
This also works on features as well.
This worked for us. Its a typical SW odd quirk.
FYI you can only change this setting if you dim a line, I tried setting this on a diameter dim. and it wouldn't let. me.