Scala plugin: @groupname @group etc. marked as "unknown tag"

IntelliJ IDEA 2018.1.1 (Ultimate Edition)

Build #IU-181.4445.78, built on April 9, 2018
JRE: 1.8.0_152-release-1136-b27 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.13.4

and Scala plugin 2018.1.9.

I have set project using Scala 2.12.4 with JDK 1.9.

When I open say Predef.scala, the IDE marks this file with 95 errors all complaining about unknown tags. Tags like @groupname, @group, @groupdesc etc.

This regression was introduced in 2018.1, previously this was not marked as error.