How to show the instruction help text on the Purchase Requisition Line DFF?(RSSP)

Summary:

I don't know why the instruction help text on the Purchase Requisition Line DFF appear in some cases and not in others.

case1).When entering an item in a list box, the instruction help text set by DFF appears at the bottom of the box.

PR screen

Setting screen

case2).When entering an item in a text box, the characters of the content of the character limit are displayed at the bottom of the box.

　　　I assumed that the instruction help text set in DFF would be displayed as in case1, but it is not.

PR screen

Setting screen