jobids, user names, and job names are sanitized when generating the job history file name. Since the name of the file needs to be parsed in the current design, a delimiter, underscore '_', was chosen. When an underscore occurs in the job id, user name, or job name it is changed to %5F like you are seeing above.
Very simply I can change the delimiter used to lessen the likelihood of percent encoding to happen. For example, dash '-' would look like this.