Playing h264 MKV PAL files with VDPAU on AMD UVD causes stalls

I have a system with an AMD Brazos processor that recently got support for the on-chip UVD decoding device with Linux. It is supposed to be accessed using VDPAU and has a Gallium state tracker for that. I try to play on this computer MKV files created from DVD RIPs (legals, I own the DVDs) that I store on a file server accessed through NFS by all our computers in our house. But quite regularly, I get "picture is too late to be displayed" messages on the console during the play until at some point, a "ES_OUT_SET_(GROUP_)PCR is called too late" occurs and the movie stalls for several second until it continues a bit later. It's worth noticing :

• The MKV can be played with issues on the same computer with Mplayer using VDPAU
• The same file on the same computer could be played without issue by VLC without VDPAU (I guess it's using XVideo in that case).
• The same file on another computer that doesn't have UVD hardware decoding abilities works without any error or even "picture too late" message.