MatthewDriver:
Stopping and starting:
The high CPU can be stopped by click File\Save (discovered by WacKEDmaN).
The high CPU can be started by click moving or resizing the Arduino IDE window.
Anyone that already his this fault is welcome to reproduce these finding and confirm it or provided an alternate view.
I can confirm this behavior on IDE 1.8.7 on windows 8.1 and windows 10 enterprise, virgin installs (no system java). Using the non-portable version, so this is certainly not isolated to portable installs.
I can also confirm that replacing the 1.8.7 "java" folder with the java folder from 1.8.5 removes the issue completely on both machines.
It seems likely that this issue is related to the bundled javavm. Others with a seperate JRE installed might not see this if the clients falls over to a system-provided jvm through PATH?