Solution : https://service.sap.com/sap/support/notes/607893 (SAP Service marketplace login required)
Summary : 
      SAP Note clarifies handling of user exits in SPAU transaction post the Basis Release 6.x upgrade. Previously, user exits were protected from overwrites during upgrades. Now, all SAP sources including user exits are replaced during upgrades, prompting them to appear in SPAU for re-adjustment. For maintaining enhancements, users should mark the user exits with a green traffic light after re-implementing enhancements via the Modification Assistant (steps include noting the exit name, resetting to the original, editing in SE38 or SE80, and reapplying the enhancements). SPAU will manage visibility for these objects in future upgrades.
Key words : 
red traffic light, green traffic light, obsolete enhancement method, symptom user exits, user exits changed, transaction spau displays, traffic light, enhancement method, user exits, transaction spau
Related Notes : 
       
| 737696 | Add. info on upgrade to SAP R/3 Enterprise 4.70 Ext. 2 SR1 | 
| 637683 | Add info about upgrade to SAP R/3 Enterprise Core 4.70 Ext 2 | 
| 587896 | Add. info on upgrade to SAP R/3 Enterprise Core 4.70 SR1 | 
| 513536 | Add. information on upgrade to SAP R/3 Enterprise Core 4.70 | 
| 381348 | Using user exit, customer exit, VOFM in SD | 
| 307189 | User exit MV45AFZB overwritten during upgrade |