BE2014: Mixed Backup vs Incremental Backup "Job Type"

I am seeing couple of my incremental backup jobs show as "mixed backup" for the job type.

I don't know why and cannot figure the differences between these incremental backup jobs with the other incremental backup jobs that show job type as "Incremental Backup" (which is what it should be).

Is it matter when it appears as mixed backup vs incremental backup?

Thanks!