I have seen this multiple times, where there are repeat entries. The top and bottom ones here are identical. I think they are different, but may just be the same one appearing again in the dictionary list. I have seen this before, and will let you know if I notice more.
Probably is a quicker way for you to run a match against all existing values with a test to prevent future duplication.
The difference between the top and bottom sentences (sentences 91 and 181328) is they have different vocab links. e.g. Sentence 91 links もう一度 as a single term, but 181328 separates it out. Deleting one would eliminate a sentence linked to the associated terms e.g. if sentence 91 gets deleted もう一度 would lose a sentence. (Probably not a big deal in this case since もう一度 has lots of sentences linked to it, but in other case might have a bigger impact)
