Just in case a few of you are experiencing this issue, I wanted to let you know what it is and how to fix it.
Recently, a bug has been noticed on WordPress when using the Google Chrome browser, which I know many of my clients use on a daily basis as their prefeered browser. This bug is only noticed in Google Chrome, so if you are using another browser, this will not apply to you.
Within the last five weeks, several people have reported an issue in the Chrome web browser that breaks the WordPress admin menu. If you hover the mouse cursor over menu items in the sidebar, they’ll occasionally fall out-of-place.
Using Chrome version 45.0.2454.85, I’m able to inconsistently reproduce the behaviour reported. Through the process of elimination, users discovered Chrome is the software at fault and not WordPress. If you are seeing this bug, it is not your website causing it.
The source of the problem stems from a new feature Google is releasing called ‘Slimming Paint’ which is enabled by default in Chrome 45. Disabling slimming paint fixes the issue.
To disable this feature, visit chrome://flags/#disable-slimming-paint in Chrome and Enable the Disable slimming paint option, and make sure the other two Enable options are disabled because they will override the Disable option.
If this sounds confusing, I would recommend using a different browser until Google fixes this issue.
Note: Unless you are very certain what you are doing, I would recommend switching browsers so nothing gets messed up.
Chrome’s development team is aware of the issue and is working towards a solution that is marked for release in Chrome 47.