QFQ

maxLength is automatically set based on the column type maxlength of the database.
addding a check if a typeahead is set resolves this issue.

if ($this->maxLength > 0 && $this->value !== '') {
    // Check if there are \r\n > those should be counted as one char, not two. #13030
    $crlf = substr_count($this->value, "\r\n");
    $max = $this->maxLength + $crlf;
    // crop string only if it's not empty (substr returns false on empty strings)
    $this->value = mb_substr($this->value, 0, $max);
}