Error "you cannot correct this posted sales invoice because item" when correcting posted invoice

Hello,
when trying to correct a posted invoice by using the correct-button I get the above message. This happens, when combined shipments for the invoice exist. The error is thrown by CU 1303, due to the fact that threre are sales shipment lines, connected to the sales invoice lines by the Shipment No.-field in Table 113. I just would like to know, if this is normal behaviour. Unfortunately, I did not find any documentation about it so far.

Thanks