Trying to interpret TERp in PostEdit Compare

I am planning to use PostEdit Compare to analyse post-edits in a large project. As a preliminary task, I edited just one of the files and created a comparison report. The edits I made were just to add "_Carlos_" to each of the MT segments in the file. I was expecting the TERp results to show only Ins (Insertions) but instead I get 8 Errors, 6 Del and 2 Sub. Is there some documentation that could help me interpret those results? Or could there be an issue related to the fact that the target language is Japanese? I'm attaching a screenshot of my results below, but I'm happy to share the entire material if needed.

Thanks in advance,