[Gambas-user] No text visible in textbox

[ron]

db records
1 "medium text"
2 "very long text to show nothing when short follows"
3 "short"
4 "medium text again"

The 4 buttons 'first' 'prev' 'next' and 'last'
Textbox1 with size of record 4 characters
txtPosit with the hResult.Index as position indicator

When 'first' followed by a serie of 'next' then if
the record 3 should be shown the textbox1 looks empty.

After click in textbox1 when it looks empty the text occurs.
If the focus (blinking cursor) stays in textbox1 and I click 
on the navigation buttons the text stays visible in that box.
I verify with second Textbox2 and the same content as textbox1

  IF hRecordData.Available THEN 
    sKey = sFLDinProc
    textbox1.Text = hRecordData[sKey]
    textbox1.SetFocus
    textbox2.Text = hRecordData[sKey]
    textbox2.SetFocus
    txtPosit.Text = hRecordData.Index + 1
  ENDIF

Blinking cursor is during navigation in textbox2 and textbox1
look still blank so .SetFocus did not help.

It occurs if a (very) long text is replaced by a short text by code.
What is wrong?

Ron