Druid - Some Shapechanges not retaining Improved Knockdown?

[Teep]

Was wondering if a DM could clarify this. If you have improved knockdown, why is it that some shapes such as Badger / Elder Dragon, Iron Golem etc remove the improved knockdown feat from your bar, and only allow you to reassign regular knockdown? Is this intended even if you have the feat? Or a bug.

Thank you!