When inserting rows/columns inside of the frozen region (to enable with
"window"->"freeze"), the freeze anchor does not get adapted and the last
row/column therefore becomes unfrozen. This is most of the times not what the
user expects. The workaround is to disable and re-enable the freeze-option with
a new anchor, but this is unnecessary work and may include a lot of scrolling.

Sample:

   [row 1]
   [row 2]
   ------------------------- (freeze border)
   [row 33]
   [row 34]

If the user inserts a new row after [row 1], the old [row2] will become [row 3],
falls out of the frozen region and will (if scrolled down) no more be visible
(which contradicts the idea of freezing rows = keeping them visible).