Thank you for your quick answer.
I've tried everything. My grid uses an alias (if I use "table" as RecordSourcetype my incremental search doesn't work).
I have two tables, one with the whole data and one with the data out of a SQL query. If I change the recordsource from one to the other table my grid looks fine. But the keypressed event out of the grid's text segment doesn't work any more.
I've tried all "workarounds" out of the FAQ document, but nothing works (even the BeforeRowColChange "trick".
My last try was (

thisform.gridrefreshing =.T.
WITH thisform.grid1
.RecordSource = ""
ENDWITH
sql_stat = "select * from tabelle where substr(upper(matnr),1,len(alltrim(thisform.text1.value)))" +;
"= alltrim(upper(thisform.text1.value)) into table c:\dummyhier"
&sql_stat
SELE dummyhier
WITH thisform.grid1
.RecordSource = "dummyhier"
ENDWITH
thisform.grid1.refresh
thisform.gridrefreshing = .F.


***************************************************************
the grids "BeforeRowColChange" contains
IF PEMstatus(thisform,"GridRefreshing",5) and thisform.gridrefreshing
NODEFAULT
RETURN
ENDIF

// Marcus