Screen Personas - Problems merging tabs

Hello experts, I hope you can help me.

I'm trying to create a flavor, merging tabs. The transaction is TM_61.

This is my flavor:

And this is the basic view:

The problem is with the part in red of the first image. I can't create o delete the quantity ("Impte.disponible" field). In the basic view, you puss create, the introduce a quantity and a date, a line is create (see in the second image), but in the created flavor doesn't work correctly.

I have seen that the problem is when I activate this flag (next image) for merging tabs. If don't activate this option all run correctly, but I can´t merging tabs.

Does exist any solution for that??

Thanks

Thanks

Arturo.