Input fields restricted on length should have maxlength parameter set
When entering the subject of a ticket/issue or writing a comment in the timelog, you can enter as many characters in the input field as you want. But if you entered more then 255 characters, this will give an error later when sending it to the redmine instance ("... too long (maximum 255 characters)").
It would be better if the HTML input field already has the maxlength parameter set to 255 then. Having this parameter set, you cannot enter more than maxlength characters into the input field. Thus, the user would immediately recognize that he cannot enter more characters instead of getting an error later when he already typed the too long input.
I just checked for the 2 mentioned input fields, there are probably a lot more of them.