Drawing problem when using 'Custom selection'

[helmut]

When using 'Edit > Set selection size > Custom selection...' for setting a selection, there is a drawing problem. Before drawing the new selection rectangle the existing selection is not cleared.

To reproduce:
1.) Open an image
2.) Use 'Edit > Set selection size > Custom selection..." and set an arbitrary selection (e.g. 50 x 50 at position 0,0)
3.) Confirm with "OK"
Repeat steps 2 & 3 with same values. You will see your selection disappaer due to the drawing problem.