Hallo Selin,
Du musst für die Maske die Eigenschaft "HTML für alle Felder generieren" anklicken. Diese Option findet Du in den Maskeneigenschaften im 2. Tab unten.
Hier der Auszug aus der Lotus Notes Knowlege Base dazu:
Data in Tabbed Tables is Lost When Web User Switches Table Tabs in Edit Mode
Problem:
On a Domino 5.x server, a web browser composes a new document that uses a form with a tabbed table. When the user enters data in a field within a tabbed table and then switches to another tab in the table, the previously entered data is lost.
Solution:
This issue was reported to Lotus Quality Engineering; however, it was determined to not be a bug. To maintain data in tabbed tables on the web, the "Generate HTML for all Fields" option must be enabled in the Form Properties dialog box. When this form property is enabled, Domino generates hidden fields that hold the user supplied data. The data is retained through subsequent actions that cause the document to be refreshed.