Just a little niggle. I've found that for some textboxes, to select them with the cursor, the cursor has to be positioned almost on the bottom frame of said box, a very small hit area, others in the same row are fine, cursor selects them when in centre of box. I have found this for three or four of my little programs.
Sorted it, afaik. I had labels above the text boxes, and I noticed that the bottom edge of some labels overlapped the top of the associated text box.
That makes sense. I was totally confused by your question but now that you mention the Labels then it makes a little more sense. :)