Steps:

1. Log in to the back office
2. Go to Product Catalog/Categories
3. Click Create
4. Type long name and identifier, for example: Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi lobortis nisl at arcu porttitor, ut tempor ex rhoncus. Phasellus interdum sem sed est porttitor, nec vestibulum odio elementum. Duis felis neque, blandit id erat quis, malesuada ultricies lectus.
5. Click Save and close

Actual result:

Error 500 is displayed: 

An exception occurred while executing 'UPDATE ibexa_taxonomy_entries SET name = ? WHERE id = ?' with params ["Lorem ipsum dolor sit amet, consectetur adipiscing elit. Morbi lobortis nisl at arcu porttitor, ut tempor ex rhoncus. Phasellus interdum sem sed est porttitor, nec vestibulum odio elementum. Duis felis neque, blandit id erat quis, malesuada ultricies lectus.", 4]:

SQLSTATE[22001]: String data, right truncated: 1406 Data too long for column 'name' at row 1

Expected result:

Field validation is on.