Currpage.LOOKUPMODE not working in page

Hi,

does anyone know why the global property CurrPage.LOOKUPMODE isn't set if the page is opened via a lookup/drilldown from a referenced field?

Example:
Open Customer Card. Click on the lookup/drilldown arrow of the Salesperson/Purchaser Code field. This opens the Page14 Salesperson/Purchaser list.
But in the OnOpenPage Trigger the property CurrPage.MOOKUPMODE is always false. (tested with MESSAGE function)

I intend to set some filters in the OnOpenPage Trigger if the page opens in LOOKUPMODE.

Has anyone an idea?
Thanks in advance

Oli