Sometimes text editors doesn't work immediately

Using XOT on my own website the texteditors doesn't work always fine.
Very offen when I click in a texteditor, the cursor will not appaer in de editor and I can't type in it. When I click twice on the sourcebutton I can use the texteditor. Very strange. It looks like the editingfield doesn't accept the cursor immediately.
Is there a solution?
Ronald