How well does ServiceReef work with Internet Explorer?
The biggest issue with IE is that they support backward compatibility with IE7 through a feature they call "Compatibility View Settings". Even if the user is on IE11, turning Compatibility View "on" will make the browser behave as if it was IE7.
IE7 was released in 2006 and hasn't been updated since early 2009. For security issues, and to enhance the end user experience, ServiceReef does not support non-modern browsers (which is in essence what IE11 becomes in this scenario).
So... in short, if you have a user in IE and they complain of something weird, have them try in another browser first (e.g. FireFox, Chrome, or Safari). If that "solves" it and they really, really love using IE and never want to use another browser... then have them go to IE Settings (the little "gear" in the upper right corner) > then to Compatibility View Settings > and turn off the "Display intranet sites in Compatibility View" check box.
That should solve a wide variety of issues, not just in ServiceReef. Unfortunately, some Microsoft programs don't even work with this "off", so their own products have issues... although I've mainly encountered that in government or large corporate environments.