Moin Ralf,
the script I posted earlier does the trick for single line fields, if  
placed on card, stack or library level. Might be adapted to more than  
one line. At least it is a workaround.
ON returnInField
     IF the autotab of the target THEN
         type TAB
     ELSE
         pass returnInField
     END if
END returnInField
Grüße,Malte