Pattern detection failing on certain patterns

I made the following test with your images.
all three images are visible in the region r.

In all cases only the right one is found (see log)

images = ("SystemHover.png", "SystemOff.png", "SystemOn.png")

r = Region(215,138,139,513)

for img in images:
  r.highlight(2)
  found = list(r.findAll(Pattern(img).exact()))
  print img
  for m in found:
    m.highlight(1)
    print m

for img in images:
  r.highlight(2)
  m = r.exists(Pattern(img).exact())
  if m:
    print img
    m.highlight(1)
    print m

--- message area
SystemHover.png
M[255,371 51x15]@S(S(0)[0,0 1440x900]) S:1.00 C:280,378 [0/0 msec]

SystemOff.png
M[259,215 49x14]@S(S(0)[0,0 1440x900]) S:0.99 C:283,222 [0/0 msec]

SystemOn.png
M[256,535 50x15]@S(S(0)[0,0 1440x900]) S:1.00 C:281,542 [0/0 msec]

SystemHover.png
M[255,371 51x15]@S(S(0)[0,0 1440x900]) S:1.00 C:280,378 [5/5 msec]

SystemOff.png
M[259,215 49x14]@S(S(0)[0,0 1440x900]) S:1.00 C:283,222 [4/4 msec]

SystemOn.png
M[256,535 50x15]@S(S(0)[0,0 1440x900]) S:1.00 C:281,542 [4/4 msec]

OK. May be it has something to do with my test environment. My code structure was as follows:
#while the button is not in on state
    #if the button is in off state, click on it
It was failing because it couldn't differentiate between the two. So when the button was in off state, it thought it was in on state and exiting the while loop.