Change in Business Partner restricted in case of Contract already activated

Hi Friends,

I have come across a very strange scenario which is described below:

I have created a RE-FX Lease Out Contract , activated the same and have carried out certain number of Periodic Postings. Now i can change the Business Partner of the Contract from existing X (for example) to a new Business Partner Y (for example).

Why would this kind of option be available in the system (I mean for what kind of Business Requirement this shall be allowed??) and how can i control that in case a RE-FX Lease Out Contract has been created and activated, nobody should be allowed to change the Business Partner in the Contract.

Has anyone come across this kind of a scenario???

Plz reply back with your valuable inputs ASAP.

Pankaj