title: IntelliJ repeatedly forgets that target src_managed is a source directory
body: <p>I am using IntelliJ 2017.1 Ultimate edition. I am working on a scala project where I generate some code using SBT. </p>
  
  <p>The code is copied into target/scala-2.11/src_managed folder.</p>
  
  <p>Time and again, my compilation fails and I see that IntelliJ has forgotten that src_managed is a source dir</p>
  
  <p><a href="https://i.stack.imgur.com/AhtbX.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/AhtbX.png" alt="enter image description here"></a></p>
  
  <p>If i right click on the src_managed folder and say mark directory as source root then compilation succeeds. But its very irritating that IntelliJ forgets time and again, that this is a source directory.</p>