[jasong]

This isn't a bug, it's how the system and preferences work.

If you look in the Data preferences, you'll also see "Default List for Single Actions", which on your system is probably set to "Create When Needed".

Below that you'll also see "Inbox items processed without a project assigned will be placed at the end of this list."

You can reproduce this without syncing by following your Steps 1 and 2, and then choosing Edit > Clean up.

Since you have an item with a context but without a project, and your preferences are set to clean up items with either a context or a project, and items without a project will appear in a single action list, your item is moved into that single action list.