IntelliJ IDEA 2016.2.4
Build #IU-162.2032.8, built on September 9, 2016
Licensed to <...>
Subscription is active until July 5, 2017
For educational use only.
JRE: 1.8.0_91-b15 amd64
JVM: Java HotSpot(TM) 64-Bit Server VM by Oracle Corporation
This should be because of something went wrong with synchronizing the build state with editor.
Clean and Build again. :))