How P41112 generates filters using form controls?

Hello community.

I have to do a customization in the P41112 program, in the form W41112A. I have to include a filter when the user put the account number to inquiry just the GL Classes that are part of that account. I tried to do it, but in the way I did it doesn't work (I created a cache to separate the GL Classes, and for each of them, I used the "Set Selection Group" system function to do filtering).

So, I tried to understand how the application do the filter when we fill the "GL Class" form control, but I checked that, even the field has "Filter Criteria" marked, and the grid has not this column, the filter works. I tried to generate a log to see se "Select" statement as well, but there was not any statement in that.