Weird error when using default params in traits

When I create a groovy method with default param in a trait in IntelliJ IDEA 14,

trait foo {
     def bar(int a=123) {
          // do something

the IDE mark this an error by red wavy line. The error msg is "default initializers are not allowed in abstract method".

However the program can run correctly. No compile/runtime error at all.

Does anybody know what's going on?