Valgrind shows "Conditional jump or move depends on uninitialised value(s)" (Bug #1535)

In this short example,

#include <opencv2/opencv.hpp>

int main(int argc, char** argv) {

    cv::Mat img = cv::imread("img.png");

    return 0;
}

valgrind is showing following output.

==7028== Memcheck, a memory error detector
==7028== Copyright (C) 2002-2010, and GNU GPL'd, by Julian Seward et al.
==7028== Using Valgrind-3.6.1-Debian and [[LibVEX]]; rerun with -h for copyright info
==7028== Command: ./a.out
==7028== 
==7028== Conditional jump or move depends on uninitialised value(s)
==7028==    at 0x620B510: inflateReset2 (in /lib/x86_64-linux-gnu/libz.so.1.2.3.4)
==7028==    by 0x620B605: inflateInit2_ (in /lib/x86_64-linux-gnu/libz.so.1.2.3.4)
==7028==    by 0x6B140A3: png_create_read_struct_2 (in /lib/x86_64-linux-gnu/libpng12.so.0.46.0)
==7028==    by 0x6B14266: png_create_read_struct (in /lib/x86_64-linux-gnu/libpng12.so.0.46.0)
==7028==    by 0x525A1DF: cv::PngDecoder::readHeader() (in /usr/local/lib/libopencv_highgui.so.2.3.1)
==7028==    by 0x52428A4: cv::imread_(std::string const&, int, int, cv::Mat*) (in /usr/local/lib/libopencv_highgui.so.2.3.1)
==7028==    by 0x5243184: cv::imread(std::string const&, int) (in /usr/local/lib/libopencv_highgui.so.2.3.1)
==7028==    by 0x400BB5: main (main.cpp:5)
==7028== 
==7028== 
==7028== HEAP SUMMARY:
==7028==     in use at exit: 8,288 bytes in 4 blocks
==7028==   total heap usage: 103 allocs, 99 frees, 129,690 bytes allocated
==7028== 
==7028== LEAK SUMMARY:
==7028==    definitely lost: 0 bytes in 0 blocks
==7028==    indirectly lost: 0 bytes in 0 blocks
==7028==      possibly lost: 0 bytes in 0 blocks
==7028==    still reachable: 8,288 bytes in 4 blocks
==7028==         suppressed: 0 bytes in 0 blocks
==7028== Rerun with --leak-check=full to see details of leaked memory
==7028== 
==7028== For counts of detected and suppressed errors, rerun with: -v
==7028== Use --track-origins=yes to see where uninitialised values come from
==7028== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 4 from 4)

The code was compiled with this command:

g++ -g main.cpp @pkg-config --cflags --libs opencv@

I believe, it is a bug or am I missing something?