Assist-Button not shown in Listpage

FragenFrager

Hello,
I have a somewhat strange problem with a newly created page.
The page displays all lines of sales offers and sales blanket orders.
The customer would like the map of the respective document to be called up when clicking on the document number.
When I now open the page via the menu, the Assist button is not displayed. However, if I call up the page directly via the object designer, it is displayed:?:
When called up via the menu, only the field appears underlined. However, I can access the map using Shift+F4.
If I set the lookup property to No, I can access the map with a mouse click. If I leave it on default, the extended overview is called up first.
The AssistEdit property is set to Yes.
Anyone an idea?