The foreground selection tool shows the area to be selected only when the zoom factor is above 50%.  When the zoom factor is below, all the image is shown as "not selected" (tinted blue).  This does not seem to affect the correct treatment of brush strokes.

Steps to reproduce:

Use foreground selection tool.
Select area, refine it (optional). 
Zoom out to 50% or less.

Expected result:
Selected area preview should render according to zoom level.

Actual result:
Everything is shown as "will not be selected" and is tinted blue (or whatever color is set).

IMHO this bug doesn't look critical/ like a 2.4 blocker.