sbt modules, doesn't detect source folders

I created an sbt project and then added an other sbt module. For the sbt module, src/main/scala folder didn't exist, so I created it manually. Even so, intellij didn't detect it as a

source folder. After I manually marked it as a source folder, in the "New" menu there were no options to create a scala class.

sbt compiles files under src/main/scala correctly.

Any ideas what might be wrong?