Hello Paolo,
This is unfortunately linked to a GDC problem in version 2.11.03 (could you confirm you are using the same version?). It has been filed in our database :
bz.#10736 => SCROLLGRID : in INPUT ARRAY, first key typed is ignored when editing field content
Normally, it should be fixed for the next release which is planned soon (in principle, first two weeks of August)
Thank you for reporting,
Best regards,
Lionel