that is an expected behaviour. certain formats like border rounding, alignment, some objects like calendar object, an even properties windows and navigation buttons will appear different depending on which client you use to visualize QV Apps. If you want that a Dashboard looks exactly the same in browser and in desktop you need to use Internet Explorer with IE-Plugin. Other browsers just have the option of ajax client,
Also it is important to note that there are some functionalities that will work in desktop mode/IE-Plugin but not in Ajax and viceversa (for example extensions and session collaboration work only in Ajax Client, while macros work only in desktop and IE-plugin).
Sometimes it can be kind of annoying but depending on the result you're looking for, then you'll need to choose between any of the available clients,