We have installed a fresh Web Help Desk version 12.8.3 (Hot Fix 2), and applied and customized the Style Sheet "Flat Buttons (12.5.1+)" but in the client view there are two buttons, History and Profile, and when each one are pressed the header changes appearance and the buttons become deformatted:

We checked and this also happens slightly in the classic Style Sheet, but with minor impact.
Someone else with this issue? Is there a way to fix this?
Thank you.