When adding a custom field to blogs, the selection of "Tree-like selector" is not honored when the new classification field is a flat taxonomy.
I have a flat set of classifications, but I do not want the user to be able to add to the set. Unfortunately, the tag-like input field allows addition of new values.
The tree-view structure is designed for hierarchical taxonomies only, when tags are flat taxonomies. You can hide the Tgas input for entering new tags by applying the following css it in the backend theme of Sitefinity. Note that this will apply the same behavior for all content types: