Hi Juan.
The problem is the following:
In the creation of the FI document, the 1st step in the code is create the consumption line (controlling level) for the ML Document. After that, the system adjust the ACCT tables of the FI Document and one of the steps is trigger the substitution (in your case, the account). In other words, the GGB1 substitution is trigger to late, at a time all the info for the ML document is ready to insert at database level Thats why you dont see the correct account in CKM3N
>>>
What I do not understand is why the system did not create a new consumption alternative when the substitution took place considering that this time there was a different G/L account.
>>> The reson is because GGB1 with HKONT is not standard, as you see the system is not intended to the substitution correctly in ML, in spite of doit correctly in FI and CO. Just for your info, if you have an account with cost element type 1 post to a cost center, you can see the substition only do its work in FI, but in CO you see an incorrecct cost element.
My option, i think its better do the substitution in badi CKML_UPDATE , in the method MODIFY_FI_TABLES. This badi is trigger very early in the creation of the FI document, before the creation of the ML Document, so every change you do here is reflected both in ML and in FI. You can read the documentation in the marketplace,
Note 996305 - Documentation: BAdI CKML_UPDATE