Variance Journal Appear in Reversal Goods Receipt of CO Production Order

Good afternoon

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

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

No problem for the first time cancellation.

Here is the example:

Step 1. We do the Goods Receipt on CO Production Order #1

Journal

     Inventory (Db)                       36000

          COGM Allocation (Cr)                  36000

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

Journal

     COGM Allocation (Db)          36000

          Inventory (Cr)                               36000

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

Journal

     Inventory (Db)                      36000

          COGM Allocation (Cr)                  36000

Step 4 (Problem). We do the Goods Receipt Reversal again on CO Production 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 "V" for this material

*No Goods Issue were made

*No Settlement Process were made

*Only this 4 transaction for this CO Production Order

Thanks in advance for your help