I installed PyCharm (Community 2016.1) on an Ubuntu 14.04 system. Whenever it is started, it would show this warning:
IBus prior to 1.5.11 may cause input problems. See IDEA-78860 for details.
PyCharm and many other IDEs based on IntelliJ IDEA seem to give this warning on Ubuntu 14.04 which uses IBus 1.5.5. IBus is a framework to enter text in multiple languages in Linux. I guess that this warning goes away if an IBus version of 1.5.11 or later is installed. But since I do not type in any language other than English, I decided to turn off IBus itself.
In XUbuntu, I opened Settings Manager -> Language Support and changed the Keyboard input method system dropdown value from IBus to None. I had to restart the system for this to take effect. The PyCharm warning went away after changing this setting.