Flac playback is still broken with the 10.0.10586.107 release of the OS. All Flac related problems for x86/x64 systems were resolved as of the 1511 release of Windows 10.
Windows 10 x86/x64 (1511) can now correctly play back 5.1 channel Flac files and high resolution ALAC audio files which is quite impressive.
It looks like there is an ARM platform problem that breaks Flac playback on Windows 10 Mobile, perhaps due to GPU usage?
Would be nice to get this resolved.
I have implemented my own player using a C++ implementation on ARM that works without issue. It's a rather long way to go to get something that works. Please fix this for the wider community of users.