Hi Taimoor,
The functionality of custom relate fields is slightly different than that of a custom relationship. While a custom relate field allows you to relate one record to the other, like you are doing between Services and Accounts, the relationship exists solely in the relate field itself. Therefore, it does not also send this connection between records down to the subpanel that was generated through the many-to-many relationship that you built out. The two operate independent of one another.
There is an article in the Knowledge Base on our support site that outlines the similarities and differences between relate fields and relationships, which may help to address additional questions you may have regarding the two: http://support.sugarcrm.com/Knowledge_Base/Studio_and_Module_Builder/Introduction_to_Relationships_and_Relate_Fields/
Regards,
Patrick Sullivan
SugarCRM Support
Thank you very much Patrick. This information was very helpful.