I wonder if the 『 are breaking the code.
It does not seems to be a problem. I have copied and pasted this last section into the itunes:summary field of the category feed and it is in the feed in full length. The feed is still valid.
But if this is no Japanese character then I would not use it.
I clear the cache before reloading a new feedvalidator page
Which cache do you clear?
What do you mean by "WordPress Summary"? The category description or the iTunes:summary of this category (the one among the Category Casting options) or something else?
The category description and the iTunes:summary of this category are to different things but they should contain them same content.