Symfony 3.4 Form doesn't react to changes in capital and small Letters, why?

Question

symfony

Hello everyone,
Today I encountered porodox, the form does not make changes if only uppercase or lowercase letters have been corrected.

For example, the database contains the following:
I change the letter to the letter, everything remains the same.
But if I change from LETTER to LETTER then everything is fine.

How can I fix it?