I'm going to explain the issue with a quick example.
I have a Folder item based on 'Folder Template', which is bucketable. I have 2 other templates - Page Template 1 and Page Template 2. The items based on Page Template 1 and Page Template 2, are actually within the Folder item as bucketable items.
I created Page Template 3 and tried to include it in Folder item as a bucketable item but whenever I create this item, it gets created as a regular item and not as a bucketable item.
Page Template 3 is essentially a copy of Page Template 2, with a few different components on it but for some reason acts differently.
Has anyone noticed this behavior?