Uppercase or Lowercase and TextArea with StyledText


If I call “EditField1.SelectedText = EditField1.SelectedText.Lowercase” or Uppercase on a selectedtext with more than one StyleRun, only the first StyleRun is maintained but the conversion is fast.
If I do :

Var i, j, k As Integer
j = EditField1.SelectionStart
k = j + EditField1.SelectionLength
for i = j to k
  EditField1.SelectionStart = i
  EditField1.SelectionLength = 1
  EditField1.SelectedText = EditField1.SelectedText.Lowercase
next i

All StyleRun of selected text are maintained but the conversion is very very slow.
Is that a bug?
How can I workaround this problem?