As a non-native speaker of a language, you sometimes fall into the rut of thinking everything that comes out of a native speaker is “correct Japanese.” This is not the case. If you think about Americans, you will know this to be true. No one thinks that rednecks are “paragons of grammar.” (Being from West Virginia, I reserve the right to make redneck comments 🙂 But they are still considered native speakers. The same is true of Japanese. There are people who are not particularly good at their own language. You will undoubtedly meet native speakers who you can run grammatical (kanjical?) circles around. However, you still have to translate their work. But in these cases, you should not feel ashamed going back to them and saying, “I simply don’t understand what you are trying to say here.” Consider that, when documents are published in English for and English speaking audience, they go through an editor. That editor picks up grammar mistakes, logical fallacies, and generally makes the document more comprehensible. However, for most of us, the documents we translate have not been edited. Rarely are they even re-read by the author (if you work in-house). So it stands to reason that these kinds of issues would occur. Just go back to the author and ask.
Note: For anyone who is experienced and reading this, I am trying to help those who are just starting. I feel like, for those of us language learners who are aware of our surroundings and of the perception other people have of us, there is kind of an uneasiness with addressing inconsistencies in a native speaker’s writing; like who am I to question a native speaker? We are always afraid that they will come back and say “You just don’t know enough Japanese to understand this,” and all the work we’ve done to establish ourselves will vanish. Silly perhaps but if you have ever tried to establish yourself as a legitimate part of a Japanese community (or in my case taken over for someone who was ethnically Japanese and raised bilingual) you will know how hard it can be to earn respect.