The official version of Blender Foundation
Sintel movie appears to have fallen foul of YouTube's
automated Content ID Matching system which checks videos for Copyright infringement - if the system finds what it thinks is a 'match' the associated video is pulled leaving the author, depending on the severity of the match, to appeal the decision. As
KatsBits found out recently this whole process results in far too many 'false positives', leaving the author to contest the decision, providing YouTube/Google see's fit to provide the option. It is not always made available and when it is, the process to getting content reinstated can be prolonged and protracted.

The more insidious aspect in this however is the Content ID systems apparent operation under the auspices of third-parties that might not otherwise be aware of what's going on in their name. And this is where the whole issue of flagging content gets very murky because
for an Copyright and/or content infringement claim to be legitimate it is supposed to be made by the Copyright owner, it cannot be done by a third-party unless said party is appointed an 'agent' for that purpose (which raises its own questions). Unfortunately YouTube/Google have yet to clarify their position with respect to Content ID operating in this way.
Equally troubling in this regard is that if YouTube/Google are acting as an third-party agent, it means they may very be in direct conflict with their claiming "Safe Harbor" under US Copyright Law which requires they not actively "police" their content or network. Failure in this regards tends to imply loss of Safe Harbor status and opening themselves up to all sorts of liabilities, something they've gone to great lengths to avoid previously, by hiding behind that very same "Safe Harbor" claim - "we don't 'police' or 'monitor' uploads or our network". For all intents and purposes it appears this is no longer the case.
The upshot here for Blender Foundation is not to bother, necessarily, with YouTube's appeal process, but rather to have their legal representative contact Sony PM&S directly to clarify the situation and, depending on the outcome of that, send legal notice to YouTube to reinstate the material with immediate effect (assuming the claim to be both false and Sony having nothing to do with any claims of infringement).
The broader picture is that now YouTube/Google
is clearly policing content, their Safe Harbor status should be questioned. Someone needs some very large brass monkey's for that though.