@psor, All renderings were done with 0.6 (hence no supersample), gcc 4.4. However the official 0.6 distribution gives the same result, so it's definitely not a problem with gcc 4.4, but maybe something system-specific. However I already checked this across three different machines (the only thing they have in common is that all of them are 64-bit Gentoo systems), and all of them have the same problem.
@Lord Crc, Did you changed anything in the blend-file (Lux-specific) before the export? What version of libpng is installed on your system? I have 1.2.38 on all machines.
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