Sorry, here's a small test project with a MP3 file and a FLAC file.

Yep, it is known. Also audio animation does not work at all for negative frame numbers as the cache doesn't support negative positions. If you use audio, do not use negative frame positions.

Sorry to tell you that even after updating to 17:2.77-1 (hash 7f03e7c), i still have the issue.

Rewording your comments so i understand: there is a known issue that audio seeking does not work well when the scene starts before frame 0. Did i get that right?
If so, i don't think the problem comes from here. I might have misled you by starting the clips before the frame 0 in the test project, but that was to show you that the FLAC clip starts from the beginning rather than from the cursor position.
I made another project with the clips starting after frame 0. They are also short enough to fit in the project length. If i put the cursor in the middle and start playing, the FLAC and OGG clips (i just found out OGG files have the same issue) play from the beginning rather than from the cursor position, and keep playing normally even when moving the cursor while playing.

Also, since Bastien doesn't have the issue, i'm wondering if it might come from another dependency. Would you like me to post the complete list of dependencies and their versions i have installed?

Eeeeh… ok, but are you using official (released by Blender foundation) builds? Please do not use thrid party builds (like distro ones) for bug reports…

Indeed, i'm using the one provided from my distro. I just downloaded the latest official build and i confirm there is no issue with it.
Thanks a lot and sorry for the bother.

would still be interesting to have the lib listing though, if issue comes from updated lib we'll likely face it too at some point.

I'll make the list whenever i have some time.
In the meantime, i opened an issue on Arch: https://bugs.archlinux.org/task/48679

Because of file size restrictions, i pointed to the second test project i posted here in order to help them reproduce the issue. I hope you don't mind.

I just found another check:

% sndfile-info test.flac 
========================================
File : test.flac
Length : 22749021
FLAC Stream Metadata
  Channels    : 2
  Sample rate : 44100
  Frames      : 10616046
  Bit width   : 16
Vorbis Comment Metadata
  title      : Move to Intercept (feat. Bit Shifter)
  artist     : Gaijin Games
  album      : Bit.Trip Beat Official Soundtrack
  tracknumber : 01
  genre      : Soundtrack
Padding Metadata
End

----------------------------------------
Sample Rate : 44100
Frames      : 10616046
Channels    : 2
Format      : 0x00170002
Sections    : 0
Seekable    : FALSE
Duration    : 00:04:00.727
Signal Max  : 16620 (-5.90 dB)

As we can see, the file is reported FALSE for being seekable...

And finally, I just found the bug report that has been submitted to libsndfile already and is fixed, so it will work again after the next release: https://github.com/erikd/libsndfile/issues/124

@Bastien Montagne (mont29) Here's the list of versions of the package i currently have, with the direct dependencies:

blender 17:2.77-1
boost-libs 1.60.0-2
desktop-file-utils 0.22-1
ffmpeg 1:3.0-1
fftw 3.3.4-1
freetype2 2.6.3-1
glew 1.13.0-1
hicolor-icon-theme 0.15-1
jack 0.124.1-6
jemalloc 4.1.0-1
libpng 1.6.21-1
libsndfile 1.0.25-3 (OK) / 1.0.26-1 (KO)
libspnav 0.2.3-1
libtiff 4.0.6-2
openal 1.17.2-2
opencollada 20150702-3
opencolorio 1.0.9-4
openexr 2.2.0-3
openimageio 1.6.10-1
openjpeg 1.5.2-1
openshadinglanguage 1.7.1-1
opensubdiv 3.0.2-3
ptex 2.0.62-2
python 3.5.1-2
python-requests 2.9.1-1
shared-mime-info 1.5-1
xdg-utils 1.1.1-1

I also made another list with all dependencies:

For the note, here's a command if you need a dependency list with version on Arch:

pactree -u blender | sort | pacman -Q -

@Joerg Mueller (nexyon) Thanks, i report this to Arch's issue right away: https://bugs.archlinux.org/task/48679