(This item pertains to the check boxes on the General tab of the Setup Options dialog box. You can open it through the F5 key or through the Edit | Preferences | Setup menu option.)
The Keep Existing Dimension's Axes check box keeps existing axes for dimensioned features from getting updated even if you switch a dimensioned feature to a different feature type. If you don't select this check box, the related dimension axes will update according to the selected feature.
By default, this is not selected.