Large Variance Appear in Reversal Goods Receipt of process Order

Hello,

Currently we face a problem that variance journal appear when doing Reversal Goods Receipt (MBST) of a process Order.

But the variance journal appear after we reverse goods receipt for the second time, third time, and so on.

And No problem for the first time cancellation.

Here is the example:

Step 1. We do the Goods Receipt on process Order #1

Journal

     Inventory (Db)                       36000

          COGM Allocation (Cr)                  36000

Step 2. We do the Goods Receipt Reversal on CO process Order #1 (with reference to Step 1)

Journal

     COGM Allocation (Db)          36000

          Inventory (Cr)                               36000

Step 3. We do the Goods Receipt again on process Order #1

Journal

     Inventory (Db)                      36000

          COGM Allocation (Cr)                  36000

Step 4 (Problem). We do the Goods Receipt Reversal again on process Order #1 (with reference to Step 3)

Journal

          Inventory (Cr)                                   36000

     COGM Allocation (Db)         54000

          Purchase Price Variant (Cr)              18000

Why Variance appear in Step 4 ? Is there any mistake ?

Note:

*We use Price Control "S" for this material

*No Goods Issue were made

*No Settlement Process were made

*Only this 4 transaction for this process Order

I've Found Some notes but It can't help me Like : 1666871 & 422606

Thanks a lot in advance for your help this an urgent and critical issue. ....