It can be fixed with regeneration, in an ugly way. I patch the generated file after it's been generated, I didn't find a better solution... It could be a bug upstream. However upstream did a major code refactoring to go to version 1.4, so there's no fix that can be cherry-picked from their git history.
But that's not the point. My concern is that if I rebuild the package with code regeneration, the diff with the current package "golang-goprotobuf-dev 1.3.4-2" is much bigger, and I'm afraid that it breaks things. On the other hand, if I just disable code regeneration, the diff with 1.3.4-2 is really minor.
So I thought that, given the timeline, it was better to make as little change as possible to this package.