After update of one of my sites to the latest Joomla 3.1.5, the backend of Joomla becomes broken. Actually, all the buttons (for Save, Edit, Update...) simply disappeared. No buttons at all! I couldn't even save the global configuration edits without editing the configuration.php file manually.
I tried to check database structure, but it was correct. When I switched to another Joomla administration template (Bluestork), it looked even more broken and without buttons as well. However, the third administrator template that comes with Joomla, Hathor, worked fine! So, I released the problem was probably related to Bootstrap which Hathor template doesn't use.
However, when I opened my site in Firefox, the browser that I rarely use these days, backend of my Joomla 3.1.5 site was fine! So, I finally started to think the problem was related to Google Chrome's cache. Several reloads didn't fix the problem though. However, when I tried to reload Joomla 3.1.5 Administrator's page with cache cleaning, the buttons were finally back to their place.
So, if you experienced the same problem, remember to reload your Google Chrome with CTRL+Shift+R (on Windows) or with Mac+Shift+R (on MacOS) BEFORE you start to dig deeper into the problem and possibly make damage to your site. All modern browsers are very fast because they are using cache intensively. But, sometimes it might cause problems, which are actually easy to solve, but only if you remember to clean your cache.