Cognito Hosted UI login form breaks state variable

Hi, I accidentally discovered a possible bug in Amazon Cognito.

My app generates a random state variable with an equal sign = at the end for the purpose of OAuth2 authorization code flow. This variable is properly URI-encoded so = is replaced with %3D and it is passed as a query parameter to /login endpoint (hosted UI). When a user fills in username and password (of an existing user in the user pool), the web form is submitted as a proper POST request. Unfortunately, the URI encoding of the state variable is lost when it is passed along with code to my redirect URL in Cognito's response.

The generated URI looks like (note the trailing =):

 http://localhost:3000/login/oauth2/code/localhost?code=4b80cf95-e454-451a-8915-52f18fbefa81&state=FvIIYVt450DT4f5SebJUOxLkY1QAWKliwy_0aXb2amQ=

I tried it in eu-central-1, I don't know if other regions are also affected.

Unfortunately the framework I'm using (Spring Boot) is pretty restrictive and doesn't parse such URI properly, throwing exception Invalid character '=' for QUERY_PARAM in \"FvIIYVt450DT4f5SebJUOxLkY1QAWKliwy_0aXb2amQ=\". Unfortunately, generating the state is out of my control without substantial effort and can not be easily overridden to avoid trailing equal sign.

Other endpoints, like /oauth2/authorize do work properly and state variable is passed to my redirect URL correctly encoded.

Is there any way how to configure Cognito so it properly encode query parameter values before redirecting browser to my redirect URL?