A new feature in AutoCAD 2013 is the Annotation Monitor which notifies the user if dimensions become disassociated. Many will find this very useful, others may not. It is controlled by the system variable, ANNOMONITOR which can be turned off by setting its value to (0). If you are not familiar with system variables, this is done as follows by typing the system variable (case insensitive) at the command line and then changing the value.
Enter new value for ANNOMONITOR <-2>: 0
The Annotation Monitor flags non-associative annotations with a yellow exclamation marker and a red plus (+) icon appears in the drawing status bar. I've listed the sysvar details from the help file below. You may want to take a look at the AutoCAD Help for more details but briefly put, the Annotation Monitor works on Dimension Objects including Leaders and Mleaders.
When changes are made to an object, for example a user has a 3D model which has been dimensioned and a decision has been made to erase (or modify it in another manner) a portion of that model. Once the model has been modified the dimensions for the modified entities are disassociated. That is when the user is notified with a marker placed next to the dimension and by the alert icon in the drawing status bar. When the user selects the marker a menu will appear with options to reassociate or delete the dimension.
A DIMREGEN may be required. From the command line:
From the AutoCAD Help file:
Turns the annotation monitor on or off. When the annotation monitor is on, it flags all non-associative annotations by placing a badge on them.
Saved in: Registry
Initial value: -2
2 -- Annotation monitor is on.
1 -- Annotation monitor on.
0 -- Annotation monitor off.
-1 -- Annotation monitor off.
-2 -- Annotation monitor off. However, automatically turns on (sets ANNOMONITOR to 2), when a model documentation edit or update event occurs.
About Associative Dimensions: http://docs.autodesk.com/ACD/2013/ENU/files/GUID-8
To Work with the Annotation Monitor: http://docs.autodesk.com/ACD/2013/ENU/files/GUID-D