Consider a type like:

     class C
     {
     }

If I add a baselist to the declaration of C and the baselist has elastic trivia, we put the baselist in the next line which is fine but the baselist doesn't get indented and results in code like this:

     class C
: IDisposable
     {
     }

To repro try running the Codefix for CA1001 or this code:

SyntaxGenerator generator = SyntaxGenerator.GetGenerator(document);
var newDecl = generator.AddInterfaceType(declaration, generator.IdentifierName("IDisposable"));