Pinned/Prioritized Posts Display Sort Unexpected Results

In version 12.0.2.17146, I am noticing that pinned posts aren't behaving as I would expect using the sort options in Forum Thread List and I'm not sure if it's a bug or feature.

In "by last reply date" I'm seeing the following sort order:

  1. Pinned Forever and unlocked
  2. Pinned Forever and locked
  3. Pinned 3 Months and locked
  4. Pinned 1 Month and locked
  5. Unlocked

In "by title" I'm seeing the following alphabetical sort order:

  1. Pinned Forever and locked
  2. Locked Posts (pinned and unpinned mixed by alpha)
  3. Unlocked Posts (pinned and unpinned mixed by alpha)

I would expect to see that all of the pinned posts are at the top of the page and either sorted amongst themselves by last reply date (regardless of pin duration or lock status) or alphabetically (again regardless of pin duration and lock status) followed by the rest of the posts sorted as appropriately below.

If this is an intended feature, could someone explain the purpose?

If this is a bug, could a ticket please be filed?