[CMake] FIND_PATH finds two out of three?

[eial at cs.bgu.ac.il]

I'm writing a program which is based on 3 external libs, Poco, ARToolKit and opencv, now the locations in the include folder is has followd:
opencv headers are in /usr/include/opencv folder, Poco headers are in /usr/include/Poco folder and ARToolKit headers are in /usr/include/AR folder.
I'm trying to find the folder in which the headers resides, but only two are returned ok, here is the code:

FIND_PATH(ARTK_INCLUDE_DIR ar.h /usr/include/AR /usr/local/include/AR)
FIND_PATH(OPENCV_INCLUDE_DIR cv.h /usr/include/opencv /usr/local/include/opencv)
FIND_PATH(POCO_INCLUDE_DIR Poco.h /usr/include/Poco /usr/local/include/Poco)

MESSAGE(STATUS ${ARTK_INCLUDE_DIR})
MESSAGE(STATUS ${OPENCV_INCLUDE_DIR})
MESSAGE(STATUS ${POCO_INCLUDE_DIR})

and here is the output: 

-- /usr/include
-- /usr/include/opencv
-- /usr/include/Poco

how can I fix this?

thanks.