When granting a title, all de jure vassals go with the title

[Matt516]

Even if I don't have "include all lower titles" selected, all lower de jure titles will go with a vassal when/if I grant them a title. For example, granting a count a duchy automatically transfers all de jure counts in that duchy to him.

 

[Dracko81]

That is intended. Include lower titles is so you can hand a duchy, several counties and the holdings to single character to deal with.