Form/Perform Not working in User Exit function EXIT_SAPLRSAP_001 !!

On R3 side, I get to CMOD to add enhancement, jump into the Exit Function module EXIT_SAPLRSAP_001, double click INCLUDE ZXRSAU01 to get into the code window, we've already got customized codes over there but without any Perform statement.

I added a Perform statement and double click the form name after the Perform keyword to get into another INCLUDE called ZXRSAF01 and defined the Form defination here. But after activated them and exit the whole exit function and then get back by double clicking the form name after the Perform keyword, it says this Form does not exist and prompt me to create this form, if I continue, I have to get to another INCLUDE called ZXRSAF02 and defined form again in this INCLUDE. I've repeated this process for three times and now the form has been defined inside the INCLUDE called ZXRSAF03. Is that a SAP bug?

Thanks