Dumping equipment master data during 122 movement from blocked stock between plants

Hello,

When we are  making the returns of serial numbered materials between two different plants with movement type 122, all the warehouse data are removed from the equipment master data. As a result, we cannot make hte 352 movement subsequently. On the other hand, when we make the same transaction with the same materials from the unrestricted stock with 122 movement type no data is removed from the equipmnet master data and we can complete the process in enhance with movement type 352. So my question is why the data from the equipment master data is removed when we make returns for the serial numbered materials with movement type 122?

Thanks in advance.