utf8mb4 charset and size of text fields

I’m trying to figure out the correct WP scheme for 4.4.2
We use separate migrations on staging before moving to prod, so need to do it manually.

I inspected the scheme at /wp-admin/includes/schema.php:60, and it does not seem to correspond to what I’m getting after upgrading the database.
So far, I noticed that upgrade script converts the tables to utf8mb4, I assume using upgrade.php:1904 maybe_convert_table_to_utf8mb4().

Some of my other installs that I inspected upgraded automatically and did not convert to utf8mb4, and I see no problems there.

But on that particular website, it does convert to utf8mb4 all native wp tables, and there are several observations I would like to share:

All the text fields that are less that longtext (i.e. tinytext, text, mediumtext) get upped one level as a result of changing the charset to utf8mb4.

So, as a result of regular “Update db” after upgrading to 4.4.2 from ~3.9.3, I get the following types in the tables:

comments.comment_author => text COLLATE utf8mb4_unicode_ci NOT NULL
comments.comment_content => mediumtext COLLATE utf8mb4_unicode_ci NOT NULL
links.link_notes => longtext COLLATE utf8mb4_unicode_ci NOT NULL
posts.post_title => mediumtext COLLATE utf8mb4_unicode_ci NOT NULL
posts.post_excerpt => mediumtext COLLATE utf8mb4_unicode_ci NOT NULL
posts.to_ping => mediumtext COLLATE utf8mb4_unicode_ci NOT NULL
posts.pinged => mediumtext COLLATE utf8mb4_unicode_ci NOT NULL

etc. the type changes from tinytext to text etc. at the time of converting table to utf8mb4 and I wonder if it is really intended.